A man doing market research knocks on a door and is greeted by a young woman with three small children running around at her feet.

The man says, "I'm doing some research for Vaseline. Have you ever used the product?"

The woman replies, "Yes, my husband and I use it all the time."

"And if you don't mind me asking, what do you use it for?"

"We use it for sex."

Taken aback, the researcher says, "Usually people lie to me and say they use it on a child's bicycle chain or to help with a hinge. But, in fact, I know most people do use it for sex. I admire your honesty. Since you've been frank so far, can you tell me exactly how you use it for sex?"

The woman says, "I don't mind telling you at all. My husband and I put it on the doorknob to keep the kids out."