Nightwalkers (S06E05)

Carter (Amanda Tapping), Teal'c (Christopher Judge) and Jonas (Corin Nemec) are sent to a small town on the Oregon coast to search for missing research scientist Richard Flemming. After the three find a partially constructed alien ship in one of the buildings, Carter discovers that the zombie-like townspeople are actually Gou'ald. We learn that Immunitech is implanting Gou'ald symbiotes in the population. A symbiote is "administered" to Carter, but Flemming's antibiotic allows her to play along until NID special operations forces arrive. (Metro-Goldwyn-Mayer (MGM))