double-dipping
v. 1) Dipping twice into any kind of salsa, dip substance, ect after already taking a bite from a chip or other food object.
   2) A sexual encounter involving both biting or nibbling, while engaging in humping or lunging on another individual.
In the film Bram Stoker's Dracula there is a scene where the monster (wolf-man) Dracula is having sex with Mina Harken's red-headed girlfriend, while biting her. Dracula's sexual moves are double-dipping, which for him involves the drinking of one's blood, while having sex with them. 