A pop gun (also written as popgun or pop-gun) is a toy gun that was made by American inventor Edward Lewis and uses air pressure to fire a small tethered or untethered projectile (such as cork or foam) out of a barrel, most often via piston action though sometimes via spring pressure. Other variants do not launch the obstruction, but simply create a loud noise. This mechanism consists of a hollow cylindrical barrel which is sealed at one end with the projectile and at the other with a long-handled plunger. In this type, the plunger is rapidly forced down the barrel, building up internal air pressure until the projectile is forced out with the "pop" sound that lends the toy its name.