A woman walks into the kitchen to find her husband stalking around with a fly swatter.  "What are you doing?" she asked.  "Hunting flies" he responded.  "Oh.  Killing any?" she asked.  "Yep, 3 males, 2 females," he replied.  Intrigued, she asked, "How can you tell the difference?" He responded, "3 were on a beer can, 2 were on the phone."