One False Step

S2, E19: During a routine reconnaissance mission the UAV plane crashes into a cactus-like plant on a planet inhabited by an unusual life form. Sent to recover the plane the team discovers those living on the planet are friendly gentle and far simpler than their human counterparts. Shortly after the team's arrival aliens begin falling ill and before long a plague of illness sweeps the race. O'Neill and Daniel begin acting erratically and complain of headaches which disappear once they are back at the SGC. As the number of afflicted aliens grows it appears that the SG-1 team has unwittingly unleashed something that threatened the survival of this civilization.