Hank: These frogs can hide their blood.

Glass frogs (Hyalinobatrachium fleischmanni) sleep during the day, which leaves them vulnerable to daytime predators. So to camouflage themselves, they snooze on leaves that are the same color as their back, and their see-through undersides help hide their outlines from predators.

However, there is one part of their bodies that they cannot turn transparent: their blood. But they managed to find a loophole. While they're sleeping, they basically put their metabolism on pause, drastically reducing how much blood needs to pump through their bodies. And instead of it being around their body, they send around 90% of their red blood cells to their livers, which are coated with sacs full of a reflective material called "guanine." The guanine bounces the light away, turning the liver into a mirror and hiding what's inside.

And then, once they start moving around, their bodies move the blood back into their bloodstreams, and they get to be little frogs doing frog stuff again. Neat trick! Very weird.

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