Butt Prints - an art project

Warning - this art project is not for those with a Butt self esteem problem.
While we were working on the swingset (the previous post) the kids were keeping themselves busy with butt art. Now, you may need to click on the images for a larger view, but here's how it works.
1. You stick your hiney in the freezing cold swimming pool.
2. You sit down on the warm cement and make a butt print.
3. Outline the print with chalk.
4. Turn it into a beautiful design. The print will quickly evaporate.

Yes, my kids are strangely creative. And our driveway is now filled with aliens, "butt"erflies, and all other sorts of buns.

My question is this. Where do they get it from? Seriously! Ryan must have been a strange child.