Hmm... special wings...
http://en.wikipedia.org/wiki/Insect_wing gives the tiniest snippet of:
"In the Diptera (true flies), the posterior pair of wings are reduced to halteres, which help the fly to sense its orientation and movement, as well as to improve balance by acting similar to gyroscopes."
Basically insects have 2 sets of wings but some flies have evolved to lose a set in place for some gyroscopes that allow it super reaction speed and manoeuverability.
At least, I hope I'm right in thinking this.

C'mon people, this is clearly very well CGI. To hit a house fly requires god like skills because flies have pretty good sensors to detect air disturbances and they have special wings that give them super evasion

Thanks if you can

Or for signitures on wills... or in general

Damn them crab bosses again! lol, evil giant squirrel...

Woo, Jason & the Argonauts! Man, I use to love those movies!