A man doing market research knocks on a door. He is greeted by a young woman with three small children running around at her feet.
"I'm doing some research for Vaseline," he says: "Have you ever used the product?"
"Yes," she replies: "My husband and I use it all the time."
"And if you don't mind me asking, what do you use it for?" he asks.
"We use it for sex," she replies.
The researcher is a little taken back. "Usually people lie to me and say that they use it on a child's bicycle chain or to help with a gate hinge," he says: "But, in fact, I know that most people do use it for sex. I admire you for your honesty. Since you've been frank so far, can you tell me exactly how you use it for sex?"
"I don't mind telling you at all," the woman says: "My husband and I put it on the door knob to keep the kids out."