The standard measure for such things is the Scoville Heat Unit, or SHU, named after Wilbur Lincoln Scoville, a chemist who in 1912 developed a method of assessing the heat given off by capsaicin, the active ingredient in chili peppers.

WSJ: The World's Hottest Chili

Cooler still is the method the arm deals with waste heat and steam: just like a regular arm, it's allowed to filter up through a permeable skin, producing "sweat" -- the same amount of perspiration you'd get on a warm summer day, according to the team.

ENGADGET: Rocket-powered mechanical arm might boost prosthetic tech