The SGC's computer mainframe is taken over by a sentient computer program from another planet. When the team tries to shut it down, it takes control of Carter instead.
"Entity" provides examples of the following tropes:
- Bottle Episode: Takes place entirely on the base.
- Brain Uploading: The entity uploads Carter's consciousness to the computer mainframe, allowing O'Neill to kill it while it's still inside her body.
- Brick Joke: O'Neill twice complains about "not getting his memos," in a callback to the previous episode.
- Contagious A.I.: A sentient program spreads throughout the base computer system before eventually jumping into Carter.
- Continuity Nod: The Planet of the Week is mentioned as being one of those from the Ancient database that O'Neill added to the dialing computers in "The Fifth Race".
- Death of Personality: Fraiser speculates that the entity may have completely overwritten Carter's brain, effectively erasing everything that makes her her.
- Doctor's Orders: O'Neill is somewhat bemused when Fraiser starts giving orders left and right after the entity first comes through the gate, only to be told that she has superiority in cases of suspected medical emergency.O'Neill: Who put her in charge?Hammond: The US Air Force. [Leaves]Teal'c: In medical matters, Dr. Fraiser may overrule those of any rank. [Leaves]O'Neill: ...I'm not getting all my memos.
- Does This Make Me Look Fat?: O'Neill makes a joke to this effect when the entity starts playing security footage of the team in the briefing room.
- Eureka Moment: Daniel has one when he realizes that Carter is now in the computer system, attempting to contact them.
- Genocide Dilemma: Subverted; O'Neill doesn't think twice about threatening to wipe out the entity's entire planet if it doesn't let Carter go.
- Nice Job Breaking It, Hero!: The heroes unwittingly damage the entity's homeworld with radio transmissions from the MALP, provoking it into retaliating.
- Not So Stoic: There are couple of instances where the cracks begin to show in Fraiser's professional calm as she's faced with the possibility of Carter's death.
- Shoot the Dog: O'Neill reluctantly zats Carter twice in order to prevent the entity from escaping. Thankfully, she is able to survive, as the entity has already transferred her consciousness to the computer mainframe.
- Sliding Scale of Idealism vs. Cynicism: Daniel insists that even if Carter is to die, it doesn't mean that she was wrong for trying to communicate with entity. O'Neill is not convinced. The episode itself leans toward the cynical side, as it is O'Neill's threats of force not Daniels negotiations that get results. O'Neill even essentially tells Daniel to shut up, because they are going to do things his way.
- Starfish Aliens: A sentient computer program that can also possess living humans.
- The Stoic: Jokingly lampshaded at the beginning of the episode as O'Neill and Daniel try to guess the expression on Teal'c's face, which remains as impassive as ever.O'Neill: You look tense.Daniel: No, I'd say anxious.Teal'c: I am neither tense nor anxious... Perhaps concerned.
- What Measure Is a Non-Human?: Before it takes control of Carter, Daniel is adamant that they should try to communicate with the entity rather than simply blowing it up, as it's obviously intelligent. Carter agrees with him; O'Neill does not.Daniel: It's obviously fighting to survive.O'Neill: So do bacteria![The entity brings up Carter's file on one of the monitors.]Carter: It's trying to communicate.O'Neill: So do bac—