Waterboarding?
Go for it.
Electric shocks?
That's nothing.
Cutting an onion?
PLEASE NO!!!
Clearly that's an exaggeration, but it really does hurt quite horribly. Ever wonder why? We can all logically put together that there must be something in the onion that gets up in the air when you cut into it. But, if you're a food geek (like the great @ForkReporter), then you might find it interesting to know what makes this happens. According to The Daily Meal, it all boils down to a few simple steps. First, you cut into the onion, exposing the enzymes in the onion skin to the air. These enzymes then turn into a chemical. This chemical floats around in the air, ultimately landing on the free nerve endings in your cornea. This hurts like super bad, so your central nervous system does its best to fight back by producing tears.
The real question, though, is how do you stop this from happening?
Option 1 - Cut the onion underwater. It's that simple. Fill a bowl with water and do your knife work under the water. This keeps the enzymes from touching the air, nipping the process in the bud.
Option 2 - Light a fire. You may have heard of Martha Stewart doing this. It hasn't been scientifically explained yet, but it may simply work because the fire sucks up all the air, pulling the fumes to the flame.
Option 3 - Vent it. It's really simple. If a fire will suck up the air containing the fumes, then you can only imagine how much better an actual powered vent will do.
Option 4 - Fridge/freeze it. You never want to store your onions in the fridge or freezer, but putting it in there for 30 minutes before cutting can slow down the chemical reaction process.
Option 5 - Keep your knife sharp. The sharper the knife, the less damaged the cells get, meaning less enzyme exposure.
Option 6 - Use lemons. Rub them on your knife blade and watch the juice cut down the fumes.
Option 7 - Don't touch your face. Don't be stupid.