Cotton mouth is not only a very dry mouth from smoking pot, but involves having small bits of mucus and spit, lining mainly the roof of your mouth feeling like cotton when you rub your tounge against it.
When you smoke with a chocolate flavored blunt wrap and have nothing to drink.
Stoner 1 and Stoner 2 toke a fat chocolate flavored blunt...
Stoner 1: Dude, it feels like theres coffee beans in the back of my throat!
Stoner 2: You must have a case of cotton mouth coffee beans.