This guy knocks on a door

One day while doing door-to-door market research, this guy knocks on a door and is greeted by a beautiful young housewife.

“Hello,” he starts, “I’m doing some research for a petroleum jelly manufacturer. Have you ever used the product?”

“Yes. My husband and I use it during make love,” she answers.

The researcher is taken aback. “Um, er, I admire you for your honesty,” he continues.

“Can you tell me exactly how you use it?”

“Sure, we put it on the doorknob so the kids can’t get in.”