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After Losing a Limb, Jellyfish Reorganize Their Bodies for Symmetry

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After losing a limb, some animals, such as lizards and salamanders, can regenerate the missing body part. Jellyfish deal with amputation in a different way: They simply rearrange their bodies to compensate for the limb they lost. This unique strategy involves reorganizing existing body parts to reestablish symmetry, a group of researchers from the California Institute of Technology report in PNAS

From left to right, the process of symmetrization, starting with the amputated state. Image Credit:Michael Abrams, Ty Basinger, and Christopher Frick, California Institute of Technology

After anesthetizing moon jellies in the lab, researchers amputated multiple limbs to see how they would regain symmetry, which is essential for their ability to move through the water. The jellyfish did so by rearranging their remaining arms and muscles, and moving their mouths to the new center of their bodies. 

The process commenced within minutes,” the researchers write. “The wound at the cut site closed within the first hours. The arms gradually spread further apart, as the manubrium [the jellyfish equivalent of a throat] relocated to the center of the body.” The jellyfish typically regained their bodily symmetry within 12 hours, whether they were placed in light or dark conditions, upside down, in groups or alone. 

To shed light on the process behind these contortions, the scientists next put muscle relaxants in the water with the jellyfish. By preventing the jellyfish's muscles from contracting, they succeeded in stopping the symmetrization process, suggesting that the action of healing after an injury is triggered by movement.

The way jellies move through the water—alternating powerful propulsive muscle contractions with more elastic movement of their jelly-like bodies—may steadily move the remaining body parts into position. “This is akin to squeezing an elastic ball at one end and producing a protrusion on the other side,” the researchers postulate. “With each cycle of compression and elastic repulsion, the arms may then relax to a new stable state.”

The true lesson here: don't try to hack a jellyfish to pieces, because they will come back to haunt you. 

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Big Questions
Why Do Cats Freak Out After Pooping?
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Cats often exhibit some very peculiar behavior, from getting into deadly combat situations with their own tail to pouncing on unsuspecting humans. Among their most curious habits: running from their litter box like a greyhound after moving their bowels. Are they running from their own fecal matter? Has waste elimination prompted a sense of euphoria?

Experts—if anyone is said to qualify as an expert in post-poop moods—aren’t exactly sure, but they’ve presented a number of entertaining theories. From a biological standpoint, some animal behaviorists suspect that a cat bolting after a deposit might stem from fears that a predator could track them based on the smell of their waste. But researchers are quick to note that they haven’t observed cats run from their BMs in the wild.

Biology also has a little bit to do with another theory, which postulates that cats used to getting their rear ends licked by their mother after defecating as kittens are showing off their independence by sprinting away, their butts having taken on self-cleaning properties in adulthood.

Not convinced? You might find another idea more plausible: Both humans and cats have a vagus nerve running from their brain stem. In both species, the nerve can be stimulated by defecation, leading to a pleasurable sensation and what some have labeled “poo-phoria,” or post-poop elation. In running, the cat may simply be working off excess energy brought on by stimulation of the nerve.

Less interesting is the notion that notoriously hygienic cats may simply want to shake off excess litter or fecal matter by running a 100-meter dash, or that a digestive problem has led to some discomfort they’re attempting to flee from. The fact is, so little research has been done in the field of pooping cat mania that there’s no universally accepted answer. Like so much of what makes cats tick, a definitive motivation will have to remain a mystery.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Animals
Listen to the Impossibly Adorable Sounds of a Baby Sloth
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Sometimes baby sloths seem almost too adorable to be real. But the little muppet-faced treasures don't just look cute—turns out they sound cute, too. We know what you're thinking: How could you have gone your whole life without knowing what these precious creatures sound like? Well, fear not: Just in time for International Sloth Day (today), we have some footage of how the tiny mammals express themselves—and it's a lot of squeaking. (Or maybe that's you squealing?)

The sloths featured in the heart-obliterating video below come from the Sloth Sanctuary of Costa Rica. The institution rescues orphaned sloths, rehabilitates them, and gets them ready to be released back into the wild.

[h/t The Kid Should See This]

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