Physicists Determined That Cats Are a Liquid

Marc-Antoine Fardin, a physicist at Paris Diderot University, was inspired by a post at boredpanda.com called “15 Proofs That Cats Are Liquids” and set out to use the tools of his trade to determine if this is, in fact, true.

Figure from "On the Rheology of Cats": (a) A cat appears as a solid material with a
consistent shape rotating and bouncing, like Silly Putty on short time scales.
(b) At longer time scales, a cat flows and fills an empty wine glass.
(c-d) For older cats, we can also introduce a characteristic time of expansion and
distinguish between liquid (c) and gaseous (d) feline states.

Rheology is the branch of physics that studies the flow of matter. Matter can come in three forms: solid, liquid and gas. Under pressure or stress, solid matter deforms whereas liquid and gas matter flows. Liquid matter is incompressible, whereas gas matter is compressible. Thus, liquids are substances that conform to the shape of their containers (i.e. are fluid) and have constant volume (i.e. are incompressible).

Flow is the process of conforming to the shape of containers and has a set duration for different substances. In rheology, this duration is called the relaxation time. The ability to determine if a substance is a liquid depends then on whether you observe it for longer than its relaxation time. Based on the evidence provided in images, Marc-Antoine determined that cats can, in fact, conform to the shapes of their containers if given enough time. Therefore, cats are liquid.

But this leaves us with additional questions about how cats flow. For one thing, some fluids are more viscous (thicker) at some times and less viscous (runnier) at others. This property is called thixotropy. Do cats exhibit thixotropy? In other words, does the relaxation time of a cat depend on its age? And do they flow with vortices or with laminar flow? A substance flowing with vortices would spin around the container and start to climb of the walls of the container. A substance flowing in a laminar way would calmly follow the outline of their container. Cats may be a fluid that can do both.

Figure from "On the Rheology of Cats": (a) A cat spontaneously rotates in a cylindrical jar.
(b) Normal forces and Weissenberg effect in a young sample of Felis catus.

Clearly, more work needs to be done on this very important question. If you have a cat, you can explore this question with some photographic evidence of your own.


Want to know more? Check this out:

Fardin, M.A. (2014). On the Rheology of Cats. Rheology Bulletin, 83(2):16-17.

The Weirdest Animals on Earth: 12 Amazing Facts About Seahorses

A seahorse in all its glory. Photo by Gustavo Gerdel at Wikimedia Commons.

1. Seahorses are fish. They include about 54 different species of fish and are closely related to sea dragons and pipefish. But seahorses are not your typical fish! A baby seahorse is called a fry (like in other fish), but a group of seahorses is called a herd (like in horses).

2. Seahorses have skeletons unlike any other fish. Unlike other bony fish, seahorses have a neck, an exoskeleton, and a prehensile tail. Seahorses do not have pelvic fins, ribs or scales. Instead, their skin is stretched over a series of bony plates arranged in rings.

3. Seahorses are terrible swimmers and can die of exhaustion if the sea is rough or the current is too strong. The only fin they have to get around with it the tiny one in the middle of their back (the dorsal fin). They use even smaller pectoral fins on the sides of their head to steer. Seahorses and razorfish are the only fish to swim upright, because it is horribly inefficient. It is a good thing they have a prehensile tail to hang on to whatever is nearby.

A pygmy seahorse in camouflage.
Photo by prilfish at Wikimedia.

4. Seahorses are experts at camouflage and can change color. They are even able to grow fleshy appendages (called cirri) that help them with camouflage by giving them a weed-like appearance.

5. Seahorses have terrible smell but amazing vision. They have the fewest genes for olfactory receptors (used in other animals for smell and taste) of any ray-finned fish species known. But seahorses have excellent vision and their eyes can work independently, meaning they can look forward and backward at the same time!

6. Seahorses eat weird. They have a toothless, tubular snout, which they use to suck up small fish and crustaceans. They swallow them whole. Seahorses do not have stomachs and don't digest very well, so they have to eat constantly.

7. Seahorses are one of the ocean's deadliest predators, with a 90% kill rate. Because of the shape of their head and their slow, finless method of movement, seahorses move with near hydrodynamic silence, barely moving the water as their stealthily sneak up on their prey. Once they are within striking distance, they snap their heads and suck up their prey. 

8. Seahorses click when they're courting and growl when their stressed. 

9. Seahorses are monogamous and pair for life. Their courtship begins with a daily dance between the couple that they do for days. The final courtship dance can last eight hours before the female "impregnates" her partner.

10. Male seahorses get "pregnant". They are the only males that take on the full responsibility of pregnancy, carrying up to 2,000 babies at a time! Although they don’t have a mammalian womb and placenta, they do have an enclosed abdominal pouch specifically for the purpose of incubating the babies. The female deposits her eggs in his brood pouch, in which he fertilizes them and incubates them for 10-45 days (depending on the species). During this time, his body undergoes a number of hormonal and physiological changes. When the babies are ready to emerge as fully developed little seahorses, seahorse dads even experience contractions as they give birth! 

11. Seahorses are evolving faster than any other group of bony fishes. Scientists have sequenced the entire genome of a tiger tail seahorse, a threatened tropical seahorse species.

12. Seahorses are under threat because of the traditional Chinese medicine trade, the pet trade, and the curio trade, all of which capture seahorses from the wild, and because of habitat depletion and pollution.

The Weirdest Animals on Earth: 12 Amazing Facts About Platypuses

What IS that? A photo by Stefan Kraft at Wikimedia Commons.

1. Platypuses are so strange, that when British scientists first encountered one, they thought it was a joke: A Governor of New South Wales, Australia, sent a platypus pelt and sketch to British scientists in 1798. Even in their first published scientific description of the species, biologists thought that this duck-beaked, beaver-bodied, web-footed specimen may be some Frankenstein-like creation stitched together as a hoax. But this is only the beginning of their oddities…

2. Platypuses are egg-laying mammals. Mammals are animals that have a backbone, are warm-blooded, and females produce milk for their young. Most females that nurse their young also carry their developing babies in their bodies and give birth to live young… But platypuses don’t play by those rules. Platypuses are monotremes, egg-laying mammals that include the platypus and four species of echidna. Most female mammals have two functional ovaries, but female platypuses, like most female birds, only have a functional left ovary. Once a year, a female platypus may produce a clutch of two or three small, leathery eggs (similar to reptile eggs), that develop in her uterus for 28 days. Because female platypuses don’t even have a vagina, when the eggs are ready, she lays them through her cloaca, an opening that serves for reproduction, peeing and pooping. (In fact, monotreme comes from the Greek for “one hole”). She then curls around them and incubates them for another 10 days until they hatch.

3. Platypuses sweat milk! Not only do female platypuses not have vaginas, they don’t have nipples either! Instead, lactating mothers ooze milk from pores in their skin, which pools in grooves on their bellies so the babies can lap it up. …And they’re not even embarrassed about it!

4. Adult platypuses are toothless. Baby platypuses (that is the actual technical term for them, by the way… not “puggles”, which would be way more fun) are born with teeth but they lose them around the time that they leave the breeding burrow. In their place are rigid-edged keratinized pads that they use as grinding plates. When they catch their prey (worms, bugs, shrimp, and even crayfish), they store it in their cheek pouches and carry it to the surface, where they use gravel to crush it in their toothless maw.

5. The platypus “duck bill” is a sensory organ used to detect electric fields. Muscles and neurons use electrical impulses to function, and these impulses can be detected by electroreceptors. Although common in shark and ray species, electroreception is rare in mammals, only having been discovered in monotremes and the Guiana dolphin. Platypuses have rows of around 40,000 electroreceptors on their highly sensitive bill, which they wave back and forth in the water, much like a hammerhead shark, to determine the location of their prey. It’s a good thing this sense is so sensitive, since they close their eyes, nose and ears every time they dive.

6. Platypuses don’t use their tails like beavers do. Whereas beavers use their large, flat, leathery tails for swimming and slapping the water to send signals, platypuses don’t use their tails for any of that. Platypuses have large, flat tails for storing fat in case of a food shortage. Unlike beaver tails, platypus tails are covered in fur, which the mothers use to snuggle with their incubating eggs.

A platypus ankle spur. Photo by E.Lonnon at Wikimedia Commons.

7. Male platypuses have venomous ankle spurs. Their venom is strong enough to kill small animals and to create excruciating pain in humans. Since only males have it and they produce more venom during the breeding season, we think its main function may be to compete for mates and breeding territories.

8. Platypuses are knuckle-walkers with a reptilian gait. Although they are well-built for swimming with their webbed feet and legs on the sides of their bodies, these traits make it quite awkward to get around on dry land. To walk, they pull in their webbing and walk on their knuckles, exposing their claws. Like reptiles and salamanders, platypuses flex their spines from side-to-side, supported by their sprawling legs.

9. Platypuses have unusually low body temperatures. As unusual as they are, platypuses are still mammals, which are defined, in part, by their ability to generate most of their own body heat with their metabolism. Platypuses do this as well, but whereas most mammals maintain body temperatures between 37-40 degrees C (99-104 degrees F), platypuses are happy with a body temperature of 32 degrees C (90 degrees F). This lower metabolism reduces the amount of calories they need to eat.

10. They have no stomach. Stomachs are specialized protein-digesting chambers of digestive tracts that contain protein-digesting enzymes and acids to activate them. Not all animals have them, but most carnivores do. The most common exceptions to this rule are fish… and platypuses. Why? We don’t know for sure, but many of these animals consume diets high in calcium carbonate, which is a natural antacid. If their own diet would constantly neutralize their stomach acid, then the stomach really isn’t going to do them any good anyway.

11. They have 10 sex chromosomes! Most mammals have two sex chromosomes, one from each parent. An individual that has two X chromosomes is usually female and an individual that has one X and one Y chromosome is usually male. Thus, female mammals pass along an X chromosome to each offspring and males can pass along an X or a Y. But platypuses are not content to be normal in any way…They have 10 sex chromosomes: 5 from mom and 5 from dad. All 5 chromosomes from mom are Xs, whereas a male sperm either contains 5 Xs or 5 Ys. Birds also have two sex chromosomes, but in birds, individuals with two of the same type are usually male and individuals with different chromosomes are usually female. Their system is called ZW, where the mammalian system is XY. The platypus X chromosome is more similar than the X chromosome of other mammals to the bird Z chromosome.

12. The platypus genome is as much of a hodgepodge as its body. Only 80% of the platypus’ genes are like other mammals. Some of their genes have only previously been found in birds, reptiles, fish, or amphibians.

To learn about more weird animals, go here.

References:

Scheich, H., Langner, G., Tidemann, C., Coles, R., & Guppy, A. (1986). Electroreception and electrolocation in platypus Nature, 319 (6052), 401-402 DOI: 10.1038/319401a0

Warren, W., Hillier, L., Marshall Graves, J., Birney, E., Ponting, C., Grützner, F., Belov, K., Miller, W., Clarke, L., Chinwalla, A., Yang, S., Heger, A., Locke, D., Miethke, P., Waters, P., Veyrunes, F., Fulton, L., Fulton, B., Graves, T., Wallis, J., Puente, X., López-Otín, C., Ordóñez, G., Eichler, E., Chen, L., Cheng, Z., Deakin, J., Alsop, A., Thompson, K., Kirby, P., Papenfuss, A., Wakefield, M., Olender, T., Lancet, D., Huttley, G., Smit, A., Pask, A., Temple-Smith, P., Batzer, M., Walker, J., Konkel, M., Harris, R., Whittington, C., Wong, E., Gemmell, N., Buschiazzo, E., Vargas Jentzsch, I., Merkel, A., Schmitz, J., Zemann, A., Churakov, G., Ole Kriegs, J., Brosius, J., Murchison, E., Sachidanandam, R., Smith, C., Hannon, G., Tsend-Ayush, E., McMillan, D., Attenborough, R., Rens, W., Ferguson-Smith, M., Lefèvre, C., Sharp, J., Nicholas, K., Ray, D., Kube, M., Reinhardt, R., Pringle, T., Taylor, J., Jones, R., Nixon, B., Dacheux, J., Niwa, H., Sekita, Y., Huang, X., Stark, A., Kheradpour, P., Kellis, M., Flicek, P., Chen, Y., Webber, C., Hardison, R., Nelson, J., Hallsworth-Pepin, K., Delehaunty, K., Markovic, C., Minx, P., Feng, Y., Kremitzki, C., Mitreva, M., Glasscock, J., Wylie, T., Wohldmann, P., Thiru, P., Nhan, M., Pohl, C., Smith, S., Hou, S., Renfree, M., Mardis, E., & Wilson, R. (2008). Genome analysis of the platypus reveals unique signatures of evolution Nature, 453 (7192), 175-183 DOI: 10.1038/nature06936

The Weirdest Animals on Earth: 12 Amazing Facts About Octopuses



Photo of a day octopus by
Ahmed Abdul Rahman available
at Wikimedia Commons.

1. The plural of octopus is octopuses. How an English word is pluralized depends, in part, on its origins. Latin words that end in –us are generally pluralized by replacing the –us with an –i (the plural of alumnus, for example, is alumni). But octopus is not Latin – It comes from the ancient Greek word októpous, whose plural is októpodes. Although octopodes is technically correct, since it has been adopted into the English language, the word is now pluralized in the English way, making it octopuses. So octopi is commonly used but not technically correct, octopodes is technically correct but not commonly used and octopussies is just plain wrong.

2. Octopuses are mollusks. This means that they are not only closely related to squid and cuttlefish, but also to clams, oysters, snails and slugs.

3. Octopuses are crazy-smart. They can solve problems, learn from watching others, use tools, and remember experiences. They even have personalities and play with toys. Check this out:

4. Octopuses have nine brains! Rather than a large centralized brain like ours, octopus brains are more like the internet. Their main CPU is a fairly small brain in their head, but each of their eight arms has an additional brain of its own. In fact, two-thirds of an octopus’ neurons are in the arms, which can independently attach to things, push things, and even smell things. They can even react after they have been severed! Not only that, but their severed arms recognize their previous owner:

5. If an octopus loses an arm, it can grow back. Those crazy arms are like the brooms in Disney's Sorcerer's Apprentice in Fantasia!

6. Octopuses are amazing camouflage artists. Their soft bodies can squeeze into ridiculously small cracks and crevices and take on any number of shapes. A 50-pound octopus, for example, can squeeze through a 2-inch hole! They can also change the color and texture of their skin to match their background.

The mimic octopus, the ultimate master of disguise, doesn’t just imitate their background, but also flounders, starfish, poisonous lionfish, and sea snakes.



A vertebrate eye (left) versus an octopus eye (right).
1: Retina, 2: Nerve fibers, 3: Optic nerve, 4: Blind spot.
Image by Jerry Crimson Mann at Wikimedia.

7. Octopuses don’t have visual blind-spots. Most animal eyes detect light patterns when light travels to the retina (the layer in the back of the eye) and falls on photoreceptor cells, causing the cells to send electrical signals through the optic nerve to the brain. Vertebrate photoreceptor cells face backwards, so their nerve fibers come in front of the retina and then exit the eye together through the optic nerve, creating a small region in the back of the eye with no photoreceptor cells. If light falls on this spot, we literally will not see it, although our brain will compensate for this missing light by imagining what should be there based on the rest of what we see. We call this our blind spot. You can test your blind spot by closing your left eye and focusing your right eye on the “R” below. Move your face towards or away from the screen until the “L” disappears. You can test your left eye by staring at the “L” in the same way.

In octopus eyes, the photoreceptor cells face forwards and the nerve fibers go behind the retina. This means that they have a continuous layer of photoreceptor cells and no blind spot.

8. Octopuses are more blue blooded than police officers. Their blood is truly blue, due to the fact that they don’t have hemoglobin, our respiratory pigment that contains iron and turns red when it binds to oxygen. Rather, they have hemocyanin, which contains copper and turns blue when oxygen binds to it.

9. Octopuses have three hearts! They have two small hearts that each pump blood through the gills and a main systemic heart that collects the blood and pumps it through the circulatory system.

10. Octopus ink is a defensive chemical concoction. It not only obscures the view of an attacker, but it also contains a chemical that irritates the predator’s eyes and temporarily paralyzes its sense of smell.

11. Octopuses bite with a bird-like beak and venomous saliva, which is mostly used to subdue prey. Of the approximately 300 octopus species, only the small blue-ringed octopus is known to be deadly to humans.

12. Octopuses die after they mate for the first time. And they mate in an odd way too: males use the tip of their third arm on the right to either insert their spermatophores (sperm packets) directly into the female’s tubular breathing funnel or he just hands it to her (The tip of the third right arm can be used to tell if an octopus is male or female). If he hands it to her, she accepts it with one of her right arms (we don’t know why they’re right-handed this way). Then the males go off to die. The females eventually lay up to 400,000 fertilized eggs, although they can wait months before they do this. She tends them and guards them at the exclusion of all else until they hatch, at which point her body rapidly deteriorates as her cells die off.