The Presurfer, in cooperation with pzzlr.com, brings you a puzzle every Monday. Just to tickle your brain.
If a cork is put into a glass of water, the cork will almost always drift to the side of the glass. There is one simple way, however, to get the cork to float in the center of the glass (the horizontal center, not the vertical). What is it? Water, the glass, and the cork are all that is required.
You can find the answer here.