Mary walks into the kitchen to find Bruce stalking around with a fly swatter. She watches for a moment then asks what he is doing. "Hunting flies" he responds. "Oh. Have you killed any yet?" she asks. He looks up and informs her "yep, three males and two females", intrigued, she asks how to tell them apart. He looks up as if the answer is obvious. "three were on a beer can and two were on the phone".