Before mirrors were invented, almost no one had ever seen their own asshole

It's funny you say that, because I was just watching a video of great apes looking at themselves in a mirror that scientists set up in the jungle. Once they got over the fear and realized they were seeing themselves, one of the things multiple apes did was look at their assholes.

I've seen my own asshole, it's not a particularly interesting view. I much prefer seeing someone else's.

Or their own bald spot.

Uhm.. any reflective surface like water would do though?