Most people don’t expect their mouth to ooze funny colors when they brush their teeth, but if they do see a little color in the sink, its usually just from bleeding gums. Add some green food coloring drops into their toothbrush to really freak them out. They may just think they’re turning into a zombie.
Whoever turns on this sink is in for a real surprise when they get sprayed in the face. Most people probably will not notice that the dish sprayer has a gum band holding down the trigger, but this will be a real spray in the face.