How do I stop playing?

In Draw Something, occasionally I'll see a message that my opponent has resigned from the game. It's nothing to do with the quality of my fat-fingered drawings, I assure you.

But I do wonder - how are they doing this? How do you resign a game? I've not seen any option anywhere. Long-clicking on a game brings up no menu, and there doesn't seem to be an option in the Gears menu, either.

I'm playing on Android, if that makes any difference.

If you swipe left on a game from the main menu, the green "Play" changes to a red "Delete" button. This will allow you to "resign" from a game and remove it from the list.