When a Jaffa was shot on Chulak the Symbiote jumped out of the Jaffa and entered Kawalsky through the back of the neck. The immaturity of the symbiote caused it to be unable to take full and permanent control of Kawalsky, who had begun to suffer from blackouts and headaches.
Kawalsky went to Dr. Nimzicki to get checked out. When Dr. Nimzicki discovered it, the symbiote took control of Kawalsky's body and responded by snapping Dr. Nimzick's neck, killing the young doctor before hiding the corpse in one of the quarters on the base. Nimzicki's body was later found by Dr. Daniel Jackson. The Goa'uld then went to the Stargate and stood in front of it, catching the attention of the others.
When he was examined again, it was discovered by Dr. William Warner that a symbiote had taken control of him, and told him that he was taking him off of active duty, when the symbiote took control, Dr. Warner hit the alarm and the Goa'uld left the infirmary.
The Goa'uld made its way to the Stargate Operations room and attempted to dial Chulak but was stopped by Captain Samantha Carter, whom he took as a hostage and attempted to leave the base. The symbiote lost control of Kawalsky and he was restrained with the intent to remove the symbiote.
Unfortunately the symbiote had already taken complete control of Kawalsky and what was removed was only a dead husk. He escaped from the infirmary, attempting to get through the Stargate. He dialed Chulak but was stopped from going through by Teal'c of Chulak. He was held in place with part of his head in the event horizon as the gate shut down, killing the Goa'uld while also ending Kawalsky's life for good although Jack later commented that the real Kawalsky had died on the operating table. (SG1: "Children of the Gods", "The Enemy Within")