Sorry about the wierd question but i watch true blood and i was wondering why when the vampires have sex with the humans they always bite them!!! Also when Bill and sookie are kissing for the first time he pulls away and like his fang pop out!!! So i guess i was wondering if it was sorta like an erection but i dont know so thats like my only guess!!! SO plz tell me the answer!! Also i understand why the pop out when they are angry so yeah!!!! Thanks so much!!!