how to tell the sex of a fly

a woman walked into the kitchen to find her husband stalking around with a fly swatter.
"what r u doing?" she asked.
"hunting flies," he responded.
"killing any?" she questioned.
"yep, 3 males and 2 females," he replied.
"how can u tell them apart?" she asked.
"easy," he said, "3 were on a beer can and 2 were on the phone."

haha

...so stereotypical...