system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why do bats hang upside down.
gpt
Hanging from the ceiling provides a more optimal position to escape harm should a predator or some other danger come along, as they can simply drop and spread their wings to be airborne instead of needing time to take off from the ground.

Also, the ceiling of a cave is less likely to encounter predators than the floor, so sleeping while hanging from the ceiling keeps them safer.