system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Are humans the only animal that cries? If so, why?
gpt
Most animals that are social have some behavior that indicates emotional or physical distress (such as your dog whining) but as far as we know the physical act of shedding tears for a purely emotional reason, and not due to irritation, appears to be a uniquely human way to express feeling a strong emotion. Chimps and other primates have vocalization and behaviors that let their group know they are experiencing distress, but they haven't  been shown to shed tears for a purely emotional reason.
Human tears serve a few purposes. The behavior (and noise) lets the people around you know you're in trouble and the actual tears help ease pain by releasing a natural painkiller called leucine enkephalin. However the jury is still out on how this natural coping mechanism evolved in humans uniquely.