How Bats Sleep Upside Down
Bats have tendons in their lower extremities, just as human beings do. However, unlike the tendons of the human body that connect muscles to bones and allow for intentional movement, the tendons in a bat's feet connect directly to the upper body. The gravitational pull on the bat's head and torso as it relaxes puts pressure on the tendons connected to the bat's feet. The pressure on the tendons pulls the bat's claws closed. When a bat wakes up and wants to hunt for food, it has to exert effort to reopen its claws so that it can take off. Otherwise, as long as the bat maintains the same relaxed, upside-down position, the claws will remain closed. For this reason, some bats remain hanging in the same position even after they die, until someone or something comes along to remove the remains.