Frogs hide nearly 90% of their red blood cells in special sacs in their livers while they sleep.
That blood can be held together for hours without clots forming. In humans, blood clots will develop at some point, say the researchers.
During sleep, the heart no longer pumps red blood, but a kind of blue fluid. When the animal wakes up, the cells reappear on their own and blood begins to circulate through the body again.
These “glass frogs” already have transparent skin, but because they hide red blood cells they become two or even three times more transparent. For example, frogs can hide completely camouflaged under a canopy.
There are multiple animals that can become transparent, but they are mostly fish. For example, the larvae of eels are transparent, and there are also glassfish and glass catfish. In water, these animals are almost invisible due to their glassiness.
