Daftly, probably, it seems like a sign of willingness, even acceptance from the girl. Love me, love my spunk. An illusion, of course, but that is after all what we're paying for. And in my experience CIM + swallow in the street (not from a steetwalker, I hasten to add) is a very considerable extra buzz. Especially with a fleck of spunk left on the cheek. Spitting it out seems a bit of an (excuse the pun) anti-climax to me.