system
Given the following post, respond as if you're commenting on Reddit:
human
Why do eyelids tend to close when the tongue tastes something really sour?
gpt
The function of the disgust expression is to stop noxious stimuli in the environment from harming us by entering one of the orifices on the face.  That's is why the nose wrinkles, the tongue protrudes and the eyes close.  

This physiological function was first proposed by Darwin (1872).