Pulling sheep ears

The term is a euphemism for masturbation. It is in reference to showing animals and conformation in the arena. When preparing goats or sheep for the proper stance, the handler will tug vigorously on the animal's ears towards him or her simulating a self pleasuring movement.

Uncle: Shay's on the phone again with her boyfriend.
Niece: Oh, don't disturb her. She might be "pulling sheep ears". She hasn't seen him for 2 months.