What evolutionary function is served by squinting one eye at lemons?

I was just watching this video of babies tasting limes and lemons for the first time, and was struck by the way they pucker their mouths and squint their eyes exactly the same way I do. And if you notice, it’s not just a cultural thing either; babies of all sorts of different ethnicities are shown reacting precisely the same way. This tells me the reaction to lemons and limes must be instinctive.

So my question is this: How does squinting one eye when exposed to a sour flavour serve to enhance the likelihood of survival? This is the only way such a behaviour could become programmed into us from the moment of birth.