How to Tell the Sex of a Fly !?

GOOD ONE ON HOW to Tell the Sex of a Fly
This is the cleanest E-mail joke I've come across in a long while!!!!!!
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A woman walked 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 them apart?

' He responded: 3 were on a beer can, 2 were on the phone.'