While the general background coloration of most glass frogs is primarily lime green, the abdominal skin of some members of this family is translucent.

The internal viscera, including the heart, liver, and gastrointestinal tract are visible through this translucent skin, hence the common name.

Check out the video to watch the heart beat within one of these frogs through its belly. Someone should do a horror movie based on this concept, I am just saying…

Photo by Heidi and Hans-Jürgen Koch via National Geographic.

Via Wikipedia.