SG - 1 returns from a mission and notices increased security at the base , but are told it is just a precaution due to a chemical tetrachloroethylene spill on Level 23 .
SG - 1 returns from a mission and ordered to the infirmary . 
 Teal'c is suspicious of the increased security , but it is told it is just a precaution due to a chemical tetrachloroethylene spill on Level 23 .