According to the Oxford Canadian Dictionary, a grimace is “a distortion of the face made in disgust or to amuse”. It’s a legitimate physical reaction. But after hours of reading, I’ve come to the conclusion that it’s rarely effective when book characters do it.
Almost every time I see this word, it draws my attention. I’m no longer thinking about the character, I’m trying to visualize a grimace. When I meet a word like this, I think: Do you use this word in everyday life? If not, maybe it doesn’t belong in your novel.
Suggestion: Use only on rare occasions, if at all.