Symmetry

Humans will subconsciously feel that a perfectly symmetrical face is inhuman due to how it is impossible for a real human to a have a perfectly symmetrical face. There are numerous reasons for why this may be the case such as a freckle or a prior injury.

Humans are however attracted to more symmetrical faces as they usually indicate good health.

This is something important to remember when designing a character. Even logos that may seem symmetrical, such as the St@r-bucks logo, have slight imperfections.