...it's belly buttons.
How do outies even happen? Innies are pretty gross too though. They're all deep and grotty looking. I've even seen people with seemingly flat belly buttons. Usually on well toned young men. They freak me out too, the flat belly buttons that is, not the young men. I'm rather fond of those.
I have to go and psych myself up for another day of abdo exams and getting close to belly-buttons. *shudders*