DD (almost 12) participated in a day long puberty course at school last week. When I picked her up she was chattering away about what they learnt (a lot of which I've covered with her already). Then she got to oral sex and my eyebrows lifted, this was a bit more info than I thought they would get.
DD: I can see this is a sensitive subject for you.
Me: Why do you think so?
DD: Because your eyes go crinkley!
This in turn left to a discussion on spit vs swallow, not a conversation I expected to have. 
Then she told me about a video clip she saw (at home) in which men were given different foods to eat and then their wives had to guess from the taste of the sperm what they had eaten. 
When I expressed the opinion that maybe this clip had not been quite appropriate she pointed out that it was part of a scientific series she watches on food... she was so matter of fact about the whole thing.
They grow up way too fast!