A woman answers the door to a market researcher.

"Good morning madam, I'm doing some research for Vaseline. Do you use it at all in your household?"

"Oh yes, all the time. It's very good for cuts, grazes and burns."

"Do you use it for anything else?"

"Oh yes, in the bedroom.

"Well madam, I am astonished with your honesty. Out of all the people who have completed our research questionaire, you are the first to admit using it for sex. Would you mind explaining for me, how you use it during sex?"

"Oh, why of course. It is quite simple really, the first thing we do is lock the door. Then we just smear it all over the bedroom doorknob, this way the kids can't get in."