I'm trying to think of a word to describe the kind of expression the face might make if you unexpectedly bit into something quite sour. It would be a kind of surprised look, eyebrows would raise, mouth might contort a bit. It's not really a wince or a flinch or a grimace or a scowl. I'm not sure if there is a specific word that fits, or if i'd just need to simply describe the look. Can anyone think of what would be right here? Thanks.