A face that has a huge smile but eyes that are not raised or wide open terrifies people because in our lizard-brain (nickname for the deep subconscious) this is actually an aggressive move of facial muscles.

We are the only ape where showing teeth can mean something positive; all other apes pull back the lips to show teeth as it's their way of showing "look what I can bite you with, fuckboy, you don't want it with me".