Killing Flies

A wife walked into the kitchen to find her husband on the prowl stalking around with a fly swatter
"What are you doing?" She asked.
"Hunting Flies" He responded.
"Kill any?" She asked.
"I sure have, 3 males , 2 Females," he replied.
"Wow, how can you tell them apart?"
His response, "3 were on a beer can, 2 were on the phone.