This week, we've got a quick and easy kickass trick that has two straws (or dollar bills... or really any two flexible tube-like objects) penetrating each other.
The setup: place one straw perpendicular over the other, with the horizontal straw on top. Make sure to hold them with your left hand from the upper-left corner.
First, wrap the horizontal straw all the way around the vertical one (make sure the loop is completed UNDERNEATH the starting wrap). Next, pull the wrapped horizontal straw up about 1/3 of the way on the vertical straw. Grab the bottom of the vertical straw and pull it around 1 and a half times, from the BOTTOM (in other words, your right hand should grab the bottom of the vertical straw, pull it underneath to the top, then complete a full revolution around the horizontal straw).
At this point, both ends of the vertical straw should be side-by-side. grab them with your right hand, and pull the remaining parts of the horizontal straw with your left. While it looks like they're in a crazy knot, you'll actually be able to pull them straight "through" each other!