My dog was showing his teeth when I was crying

I've never asked anything on reddit but today I was crying and petting my dog and he was looking at me and was showing his teeth. He didn't bite me or anything. I've never seen him do that before he is very sweet and never harmed anyone. Idk what breed he is sth like Labrador retriever mix… So what am askin is if thats sign of empathy or he feels uncomfortable or sth like that. Has anyone experienced it? Might be dumb question but im curious.