These glass frogs have a clever way of hiding from predators during the day: they sleep on leaves that match the color of their backs, and their see-through undersides help hide their outlines. 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 put their metabolism on pause, drastically reducing how much blood needs to pump through their body. Instead, they send around 90 percent of their red blood cells to their livers, which are coated with sacks full of a reflective material called guanine. The guanine bounces the light away, turning the liver into a mirror and hiding what’s inside. Once they start moving around, their bodies move the blood back into their bloodstream and they can go back to being little frogs again. Neat trick! Very weird.