Or you could NOT do that.

Your brain needs oxygen...and when you do it like that, you fuck up A LOT of braincells.

The proper and 'safe' way to do it is...

1. Fill the balloon.
2. Inhale half of the nitrous.
3. Pinch balloon and exhale and breath in oxygen then exhale.
4. Inhale the rest of the balloon.
5. Exhale.
6. Experience the best high in the world.