lol, i do this sometimes.
also if u chew ur fingernails or chew gum u prob weren't satisfied enough/ didnt get breast fed enough when u were a baby. (its hard to describe correctly, its not a bad thing, its just a habit that can happen because u subconsciously feel a need to hav something in ur mouth because u feel like u missed out wen u were a baby)
and overstrict toilet training can cause OCD or can also cause rebellious personalities
that's my "fun" fact for the day