http://www.bbc.co.uk/science/humanbody/sleep/sheep/reaction_version5.swf
.2222
Good enough for me, and not exciting enough to keep my attention much longer than 5 attempts.
I was half expecting a screamer though …
I have to say that visualizing this is an excellent way to get to sleep! Minus the evil darts, of course. Just listen to the cute little noises and watch the sheep as they wander off. Nothing could be more bucolic and restful!