The frog that hides its blood when it sleeps

Researchers studying Fleischmann’s glassfrog found an extraordinary sleep trick: the animals can remove about 89% of their red blood cells from circulation and store them in the liver, making their bodies more transparent. Blood normally scatters and absorbs light. Temporarily packing those cells away helps the frog become less visible against greenery. It is a beautiful natural solution to a problem that biologists are still trying to understand fully. One detail worth keeping straight: glassfrogs are a group, and the famous blood-hiding experiment studied a particular species. The picture here shows a related glassfrog, not the exact animals in the experiment. If you love creatures that seem invented, start with glassfrogs. Then watch how many extraordinary survival tricks appear once you look a little closer.