I'm in my mid 30's, and two days ago I found out that male dogs piss with a leg raised, and female dogs piss sitting down. I always thought all dogs (male and female) just switch it up, going with whatever they feel like at a given moment (maybe the raised leg usually for claiming territory, and the sitting down generally for the actual job).
I found out when my wife's friend brought her dog over, and we were forced to watch it run around the garden like a maniac and piss on each and every object available. I try to make some small talk and ask the friend if the dog is male or female, my wife states that its pretty obvious the dog is male, and I ask her how she can tell. I've never seen concern, pity and fear come together in one reaction like that.
Any other blind spots in general knowledge that came to light embarrassingly late?