This is a clever and engaging version of Galton's Quincunx. It shows the underlying theoretical distribution (a normal curve) as well as the results of dropping mice into the quincunx.
http://www.mathcats.com/explore/bag-o/mice.html

Here is a similar activity (not as cute though). Set them both running and compare...
http://probability.ca/jeff/java/utday/

A wonderful interactive version of this classical device.
http://www.subtangent.com/maths/ig-quincunx.php