Michael Smith-Welch, "Pool Piece"
(Olafur Eliasson and Rebecca Horn stole this piece from
Finnbogi Petursson. I'm stealing it back.)

A pool of water reflects a beam of light from a spotlight onto a white screen. Two choices: Sit and contemplate the water as it reflects gyrations of light on the screen; or, play with the pool, the water, or the spot light and change the behavior of the work.