system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 What causes the involuntary scowl when we eat something unexpectedly bitter?
gpt
I think it was Steven Pinker who said that it's probably an evolutionary defense mechanism. When you taste something unexpectedly bitter you tend to make a face and stick your tongue out (children start doing this very early). This is probably a mechanism to eject any of the substance still in your mouth. Not really any evidence though so it's just conjecture.