It works like this: twelve players in turn see either a phrase or a drawing. They then describe the drawing, or draw the phrase. The material is then passed anonymously onto the next player.
The game handles all the team details, passing items anonymously from one player to the next. In the end, your app updates and you can view the entire twelve-part sequence.
Here's an example of a sequence I participated in.
What made this sequence stand out from the others, and made it "filmable" for consumption by a TUAW audience, is that it did not contain any off-color phrases or sexually-explicit material.
That made it the exception.
Although participants can report inappropriate sequences, apparently most users don't care and are apparently gleefully sharing their wild humor with others.
I have no idea why this app has a 4+ rating. I strongly encourage parents to limit access to children. As for teens and young professionals, well, you know what you're getting into. It probably plays better with beer.
The app crashed several times during use, the drawing tools are pretty awkward to use, but if you want to go all Beavis and Butthead well, this is the app for you.