these victims in these videos. sarin kills you by breaking down your nerves. then you suffocate. as for these other visual signs, they are very consistent with signs. a chemical weapons expert from the center for nonproliferation studies says if you don't have a gas mask on when an attack occurs, within minutes your body will begin to shut down. the things you see in these videos, the twitching, convulsing, difficulty with vision and foaming at the mouth, all consistent with sarin. if you don't have a gas mask on and you are exposed to a concentrated amount of sarin, here's a quote, your body will short-circuit, you will die within minutes. don? >> because of this, is this why they are so confident -- is this what makes them so confident about the type of chemical weapons used? >> reporter: that's part of it. but you have to also understand how they test for sarin and how they can be very confident in the samples that they take. experts say that these u.n.