National Geographic Humanly Impossible The Glass-Eater: Extreme performers such as glass eaters and sword swallowers push the human body to extraordinary limits. But how do they do it? Humanly Impossible follows a team of doctors and scientists to reveal the physiology behind bizarre and dangerous stunts that surpass average human capability. Doctors investigate The Great Nippulini to find out how he lifts up to 70 lbs. using only his nipples.