How do you get that effect black rancid mouth?

I'm a zombie to hallow … well done for the opening of Zombieland, and I'm excited my makeup looks great, but I want the effect rancid black mouth where my gums and teeth are rotten, how I can do. If you do not know I speak, youtube undo redo (Zombie Strippers) has a very good example …

Food coloring should

Zombieland ‘Wichita’ Makeup tutorial