Baby-bottle nipple business 

  A guy is going on a tour of a factory that produces various 
  latex products. At the first stop, he is 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 the needle poking a hole in the end of the 
  Later, the tour reaches the part of the factory where 
  condoms are manufactured. The machine makes a "Hiss. Hiss. 
  Hiss. Hiss-pop" noise. "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 
  "Well, that can't be good for the condoms!"
  "Yeah, but it's great for the baby-bottle nipple business!"