Why do we squint when tasting very sour things? Sometimes while tasting a very sour thing (like tamarind, lemon etc.) our eyes squint immediately and involuntarily for a second, but a little later becomes normal again. Why, and how, does this reflexive movement occur?

Maybe it serves to show others that we may be consuming something poisonous. We cry when we are sad to alert others of our distress. There may be better ways to show something is poisonous, but a child doesn't have any real way to alert who ever is feeding it that it may be poisonous. If I was feeding my baby something, and they had that reaction, I would not give that to them again.