I don't know man. His sister definitely took it too far, but I still feel a LOT of guilt for doing something similar with my sister. I've tried to block it from my memory, but my sister was 5 and I was 4. I don't know how my sister got the idea, but yeah...we ended up...you know...licking
I know she remembers too but we've never talked about it since. Its a mutual "never bring that up or I will kill you"