This would be pretty funny for you to do to the kids. You'll be down anyways since it's your dads birthday, and this would make you laugh all day! prank Blue teeth/ numb mouth- put a small drop of food coloring in center of toothbrush. Make sure to use the same color as the bristles. ALSO, you could put some oragel numbing gel deep in the base of the bristles... one of my FAVE'S!