Why do you cry when you cut onions?

And more importantly, how can you prevent it from happening . . . if you can.

Onions contain a lot of sulfur. When you cut them, the cells burst and release enzymes. These enzymes turn sulfur into a gas. The gas into your eyes and forms sulfuric acid. One way to prevent the tears is to rub a cut lemon on the knife. Watch the Mythbusters prove it here on YouTube