Clam Beat
The rhythmic pulsation of the female genitalia in response to stimulation via either an external source or in some cases the mere thought of a sexual encounter. This phenomenon is usually accompanied by the excretion of bodily fluids stated colloquially as "clam chowder."
At first I didn't think Jackie was that in to me until the clam beat started up, from there on out it was like Ivar's up in the bitch.