Harrison investigates the stuff that holds us in: skin. With help from a special-effects make-up artist, he finds out the science behind scabs and bruises, and even learns how to make cool fish-monster scales. “How come humans don’t have scales?” Are parts of our skin more sensitive than others? Blindfolded challengers have to identify mystery objects rubbed against their foot, leg, and hands. Harrison goes to the beach with a skin scientist to test how sunscreen can protect UV-sensitive Frisbees from turning purple.