Geez don't you girls watch pornos?
"snowballing" is when two girls are blowing a guy, he cums in one of their mouths, and she spits it into the other girl's mouth. Yes, I've seen videos. No, I've never had it done in front of me. Personally I think it's the same deal as a facial, as in, it really does nothing for me (because I've already cum...I'd rather have the girl have really talented bj skills instead of liking cum spit in her mouth) but to each their own.
I DOUBT if I would partake in real life, because I would say that is rather high risk behaviour. But hey, whatever.