Onions, some make you ball your eyes out and others do absolutely nothing. There is a very boring scientific reason that involves chemicals being released when you chop them. To keep it simple it all depends on the soil they have grown in, thats why some make you cry and others have no effect.
Here is how to prevent the release of the gases getting into your eyes. You could wear onion goggles:
But even they sometimes don't work. Thats because when you breathe the gases in through your nose they effect your sinuses which in turn makes you cry. So unless you want to buy onion goggles and wear a nose peg every time there really isn't an easy solution.
Running water or having a fan near where you are chopping your onion actually helps prevent the gases going straight into your eyes.
THE MATCH STICK TECHNIQUE
Recently Carrie found a technique that actually reduces the tears. How does this work?
*I'm pretty sure there was a typo......breathing!