Tetrachloroethylene is a chemical used on Earth to aid in the cleaning of clothes without the use of water. It is volatile, stable and non flammable. Inhaling its vapors (particularly in closed, poorly ventilated areas) can cause dizziness, headache, sleepiness, confusion, nausea, difficulty in speaking and walking, unconsciousness, and death. Tetrachloroethylene was used as a cover story in order for the Stragoth to invade Stargate Command in 1999. (SG1: "Foothold")