This is the coolest invention ever. I learned about it on America's Test Kitchen on PBS. It's basically a crank that fits through a peanut butter jar-shaped lid with a gasket in it. You put the crank through the lid and the gasket, screw the lid onto a jar of natural peanut butter, and crank several times until the peanut butter and oil are mixed together. No oil spillage, no waste, no mess. The best part is when you draw the crank out through the lid, it comes out completely clean! There's a teeny bit of oil left on the gasket, so you just wash everything with dish soap and it's ready for the next time. Totally recommend this if you eat natural peanut butter or other nut butters that don't have stabilizers like hydrogenated oils to keep them together.