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.
To illustrate the commonalities between sour (#1), disgust (#2) and pain (#3) I would like to share the following web finds.
PS: I am not a psychologist - Consider my contribution as an educated guess.
Squinting is the organism's way to warn us that we are eating something that could eventually be dangerous, acidic or toxic. It's a reflex, developed many many years ago when the ancient people did not know much about the safety of plants, roots and other foods. They used to try them and decide if the object is eatable or not according to its taste.
Also, our tongue has very sensitive papilla, which react to sourness and make the muscles contract.
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