Brushing your teeth is pretty mundane. Why not enliven the experience for a friend or enemy by pranking them into thinking that their mouth is gushing blood? This video will teach you how to use food coloring and an oven to set up the Bloody Toothbrush Prank. All you do is cook the food coloring into it's powdered essence, apply the powder sneakily your victim's toothbrush, and wait until they brush.
CAUTION: Powdered food coloring is strong, and will stain the skin for days. Be careful when preparing, and choose a good sport as your victim so they won't kill you.