2 Macy's is rumored to be the second-largest helium customer in the world — Curse you, Red Baron! — but the element is used for more than just floating things. Two quick examples: It's perfect for pressurizing space shuttle fuel tanks (only helium remains a gas at the frigid temperature of liquid-hydrogen rocket fuel) and for cooling the superconducting electromagnets in MRI devices (helium boasts the coldest liquid state of any element).
3 Inhaling helium lets you croon like Alvin & Co. because the gas is only one-seventh as dense as air. When helium is streaming out of your lungs as you yodel, the sound waves produced by your vocal cords travel much faster, which alters the tone quality of your voice. The result: that endlessly funny squeak.