The answer? NOTHING. Besides emitting a very annoying high pitched sound, and lighting up.
So, you might as well give your cats Christmas tree lights to play with, which have the bonus of being silent...and we don't do that, do we? Which begs the further question, what were these people THINKING?
The cat verdict was no less scathing. Both Ava and Kato spared it just one glance - a mingled look of disgust and wariness. And walked off.
It's a colossal gong from us.
If you have money to burn and want to try it for yourself, I found it at ebay: http://www.ebay.com.au/itm/AMAZING-CAT-TOY-MARS-CATS-CANT-RESIST-/380367230921