A fellow is going on a tour of a factory that produces various latex products. 
At the first stop, he's shown the machine that manufactures baby-bottle 
nipples. The machine makes a loud hiss-pop! noise. 

"The hiss is the rubber being injected into the mold," explains the guide. "The 
popping sound is a needle poking a hole in the end of the nipple." 

Later, the tour reaches the part of the factory where condoms are manufactured. 
The machine makes a noise: 'Hiss. Hiss. Hiss. Hiss-pop!" 

"Wait a minute!" says the man taking the tour. "I understand what the 'hiss, 
hiss,' is, but what's that 'pop!' every so often?" 

"Oh, it's just the same as in the baby-bottle nipple machine," says the guide. "
It pokes a hole in every fourth condom." 

"Well, that can't be good for the condoms!" 

"Yeah, but it's great for the baby-bottle nipple business!"