system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do flys rub their hands together menacingly whenever they land?
gpt
They get dirty and have flavor receptors (think taste buds) on their legs. They rub themselves off in order to eat and be able to taste it.

**Edit:** Alternate theory - They know something we don't. *Half Life 3 confirmed!*