While going down on a girl, the other person (male or female) inserts his/her index fingers into the vagina. He/she should then make circles (one clockwise and one counterclockwise) with their fingers while stimulating the clitoris. This motion mimicks that of an egg beater.
Jon: What did you do last night?
Mike: I was with this girl. She didn't want to have sex, but I totally gave her the Sacramento Egg Beater