system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it that animals such as a bat or sloth can hang upside down for long periods of time but a human cannot?
gpt
Humans would suffer because we haven't evolved to maintain that position for very long, and blood would struggle to flow correctly, and begin to pool in the head. Bats and sloths by contrast have specialized valves and muscles to compensate for gravity when they're inverted. In their case blood is still distributed correctly, and doesn't just pool in the head.