'Head On' by Cai Guo-Qiang at the Deutsche Guggenheim in Berlin.  The installation consists of 99 life-sized wolves, fabricated from painted sheepskins and stuffed with hay and metal wires, barreling in a continuous stream towards - and into - a glass wall.  Only the first ones crash into it, but the pack chases after the leader.

http://www.we-make-money-not-art.com/archives/008905.php - (link my time-out over time)