Pulsating circles

Today I had to do homework again. Not for myself, but for my girlfriend, Anna Kröger. She came up with the idea of black an white outlines, continuing outwards from a certain shape. In addition to paintings and drawings she thought it would be fun to do an interactive animation. This is where I came in. We came up with the following animation. Hover your mouse over a circle, or click one, and see what happens.

circles