Bats sleep upside down, hanging by feet whose tendons lock shut without muscular effort.

The longer version

A bat's toe tendons run through a rough sheath so that body weight pulls the tendon and jams the claw shut. Hanging therefore costs no muscular effort, and the animal can stay suspended even while deeply asleep or hibernating. Blood pressure in a hanging bat is low enough that gravity does not cause the pooling a large animal would suffer.

The posture also suits a body built for flight: bats cannot launch well from the ground, so dropping from a perch lets them fall into flight. Roosts in caves and hollows shelter large colonies that hang together for warmth. Hibernating bats may stay suspended for months without moving, which the locking mechanism makes possible.

Where this entry sits

This collection gathers curious details about sleeping and dreaming, from nightly brain stages and body clocks to naps, yawns and unusual animal habits. It also covers how bedtime customs have changed across centuries, without offering any advice. The full list sits on the Sleep and Dreams page, where every entry is listed in order.