Nerotoxin

Nerotoxin is a deadly posinus gas that is sparyed around in portal's final level in a vain attempt to kill you.

 *Cough* Nerotoxin...so deadly...Choking...*Laughter* Im Kidding!

I could take a bath in the stuff, put it on cereal, rub it right into my eyes. Honestly, it's not deadly at all. To me."