This is an extremely easy glitch to do, but only works in the original Duke Nukem 3D for DOS and variants.(Plutonium Pak, etc.) Simply select Weapon 1(Duke's Foot) then hold the Fire button. As you're doing this, hold down the Mighty Foot button as well. Duke is now kicking 1.5 times per kick! Not only that, but he's doing so using both his left and right feet at the same time. How gravity defying.