"Wait a minute, I'm not hungry or thirsty. Why not? ...Because I'm dead?!"
— Dr. Daniel Jackson
Daniel is rendered invisible and intangible after being exposed to radiation from a Crystal Skull found on another planet, and is forced to seek help from the only other person with experience of such technology — his estranged grandfather, the archaeologist Dr. Nicholas Ballard.
"Crystal Skull" provides examples of the following tropes:
- Adventurer Archaeologist: It's implied that Nicholas Ballard was one in his youth, though his Glory Days are now long behind him.
- Chroma Key: The cavern has
not aged well since 2000. - Crystal Skull: Duh. Incidentally, many crystal skulls are now believed to be fakes manufactured in 19th century Germany. The episode possibly makes a nod to this when Rothman suggests a 19th century German origin for the crystal skull from P7X-377.
- Deadpan Snarker: Daniel really dials up the snark in this episode due to his increasing frustration over his inability to make himself seen or heard.
- End of an Era: Meta Example. This was the final episode of SG-1 to be shot on 16 mm film (which had been the celluloid norm since the Pilot). Beginning with the next episode, SG-1 would upgrade to 35 mm film.
- Enemy Mine: When the alien appears it says something in Mayan that apparently translates to "the enemy of my enemy is my friend." Daniel realizes that the "enemy" they're referring to is the Goa'uld when the skull fails to transport Teal'c and uses this to earn their trust.
- A Father to His Men: Demonstrated when Daniel overhears Hammond on the phone with his granddaughter, telling her that he can't come to her school play because "a very close friend of his is lost and needs his help."
- First-Name Basis: The rest of the team seem to find it a little odd that Daniel refers to his grandfather as "Nick", to which Daniel replies that Nick had always insisted on it, even when he was a young child.
- Foreshadowing: The fact that Nicholas can see Daniel is brought up before it's even mentioned, because Nicholas looks right at him and makes eye contact when Daniel enters the meeting room.
- Generation Xerox: Both Daniel and his grandfather are once-respected archaeologists who were laughed out of academia for outlandish theories that would later turn out to be true. Tragically, neither of them believed the other's story which is why they're estranged for so many years until this event makes them realise they were both telling the truth.
- Intangibility: Daniel is rendered intangible thanks to Teal'c zatting the crystal skull as it starts to activate.
- It's All My Fault: Defied by Daniel when Ballard tries to tell him he wasn't to blame for the death of his parents:Daniel: I was eight years old, how could it be my fault?
- I Warned You: When O'Neill attempts to leave the infirmary while still suffering the effects of radiation sickness:Teal'c: Dr. Fraiser believes you are not strong enough to undertake such a mission.
O'Neill: Yeah, whatever.
[he attempts to get out of bed and promptly collapses on the floor]
Teal'c: Dr. Fraiser is usually correct in such matters. - Malaproper: O'Neill calls neutrinos "nintendos" at one point. Although knowing O'Neill it's likely a case of Obfuscating Stupidity.
- Mathematician's Answer: Teal'c is quite matter-of-fact when trying to convince Gen. Hammond to send him back to the planet:Hammond: And if that thing zaps you to wherever it sent Dr. Jackson?Teal'c: Then I will have succeeded in locating him.
- Multitasked Conversation: Ballard pulls this when Daniel calls him out for manipulating him, responding in such a way that O'Neill thinks he's talking to him:O'Neill: Daniel said you should come along to make it work.
Daniel: Wait, I never sad that. You're taking advantage of me.
Ballard: Yes. - The Napoleon: O'Neill calls Fraiser a "Napoleonic power-monger", as a reference to both her height and the iron fist with which she rules the infirmary.
- No One Gets Left Behind: After Daniel disappears, Teal'c returns to the planet to search for him as soon as he is physically able to do so, despite not getting a clean bill of health from Fraiser. Daniel thanks him for this, realizing that he may not have been able to get back to Earth if Teal'c hadn't done so.
- Plausible Deniability: This was the reason why they were allowed to bring Nick to Stargate HQ to see the crystal skull. He as a disgraced archaeologist whose theories were discredited and had been in a psychiatric hospital for about 20 years. Who would believe him?
- Raised by Grandparents: Discussed. It's been known from the very beginning of the show that Daniel went through foster care because his parents died when he was young. This episode reveals that he does have a living grandfather, but was not raised by him because Ballard was too busy travelling the world to look after him. It was that decision that put Daniel into foster care; Daniel is still a little bitter about that.
- Something Only They Would Say: O'Neill is inclined to believe that Daniel is present and communicating through his grandfather only when Daniel insults him:Daniel: Repeat what I'm saying: I'm standing right beside you.
Ballard: He's standing right beside me.
O'Neill: He's lost a few pounds.
Daniel: [to himself] Jack, don't be an ass.
Ballard: Jack, don't be an ass.
O'Neill: ...Daniel? - Stay with the Aliens: Ballard decides to stay behind when the aliens request that he join them, as he's spent the last thirty years trying to prove that the crystal skull works.
- Stupid Scientist: Rothman is portrayed as such in his attempts to figure out how the skull works, offering increasingly unhelpful suggestions while Daniel snarks at him and the rest of SG-1 grow ever more impatient. Even Siler gets fed up with him.Rothman: Well, it -- it's a crystal skull.
Hammond: We knew that, Doctor. - They Called Me Mad!: Much like his grandson, Ballard was ridiculed for his theories involving aliens, though he took it a step further than Daniel and suffered a mental breakdown that got him committed to a psychiatric hospital as a result. For added irony, neither Daniel nor his grandfather believed the other's theory and dismissed each other as insane, while in actual fact they were both right.
- Trick Dialogue: An odd example where both Daniel and Ballard are present, but Daniel assumes Ballard can't see him and is merely thinking aloud while Ballard believes Daniel to be a hallucination. They actually manage to have an entire conversation in this manner before they realize they're responding to one another.
- Trust Password: Daniel has Ballard mention Kayla's school play to convince Hammond that he's in the room, since Hammond believed himself to be alone in his office when he had that particular phone call.
- What Happened to the Mouse?: Aside from an oblique reference to a Dutch grandfather two episodes later, neither Daniel's grandfather nor the giant aliens are mentioned again until season Ten, fully seven years later!
- Though Daniel once did briefly mention that in his youth, Nick once conducted an expedition to Central America to find the Foutain of Youth.
