A New Zealand Charity has created a website that allows you to edit YouTube videos and add fart noises to them at opportune moments. The site is simple to use and aims to raise awareness of .Bowl Cancer, you can test out the YouTube fart machine at http://www.bumsarefullofsurprises.org.nz.
The ad was put together by Whybin\TBWA, Auckland. If you want an example I spend a few minutes crafting one using a bizarre new Ariel ad from Japan, have a look at http://www.beatbowelcancer.org.nz/fartbomb/video.php?id=531.