The Magical Cut

The guy from The Action Lab cuts his hand with a plastic butter knife and manages to draw blood. Or does he? This is the magic of chemicals. He's got ferrochloride and potassium thiocyanite on each side of the knife, and they combine when he presses it against his hand. That makes the blood, and then the addition of sodium fluoride makes it all turn transparent again. You might think this is genius way to do fake blood for a movie scene, but honestly, the cost of the chemicals is probably much more than what you'd pay for professional fake blood packets. (via reddit)