When General Hammond is talking to his granddaughter, he is using the red phone which is supposed to be a direct line to the President. He should have used his other phone.
When SG-1 entered the cavern with Nick, you can clearly tell that they are against a green screen, as when they start to cross the catwalk to the skull, the rocks above passed through Teal'c's head.
Trivia: This episode marks the first appearance of Dr. Robert Rothman since "Forever In A Day." However, Daniel dreamed that story. So exactly when did SGC actually hire Rothman?
When Daniel is out-of-phase, he can seemingly pass through solid objects. As is often the case in sci-fi shows, however, there's no explanation for how he can lean against the wall outside the elevator that Samantha gets into, sit on a cabinet in the control room, and stand on the floor throughout the entire episode.
When Nicholas Ballard is "alone" in his quarters with invisible Daniel Jackson for the first time at the SGC and confesses that he can see and hear him, Dr. Jackson has a frustrated but excited outburst in which he touches a chair which is knocked slightly back. He should have passed right through it.
When Daniel first comes back to the SGC as a ghost, after he waves his hand through General Hammond's head the CGI made his fingers extremely pointy and can be clearly seen when he is looking at them.
Jack: Look, I'm sick of laying around. Help me up.
Teal'c: Dr. Fraiser believes you are not strong enough to undertake such a mission.
Jack: Yeah. Whatever.
(tries to get up, but instantly falls to the floor)
Teal'c: Dr. Fraiser is usually correct in such matters.
(Jack and Sam call it a night, as ghost-Daniel looks on)
Daniel: What? That's it! What ever happened to working through the night? I do it for you.
Sam: Do you get the feeling that Daniel's still around?
Sam: I guess it's 'cause we miss him.
Jack: Or radiation sickness.
Nick: Now we must wait for the giant aliens.
Jack: That just has a nice ring to it.
Rothman: Teleportation device...? I... what do you think?
Siler: I think you're gonna get fired.
Jack: He's just a little anxious to see ol' Nick.
Nurse: Oh, are you close?
Teal'c: (overlapping) No.
Jack: (overlapping) Yes.
(Jack stares at Teal'c)
Teal'c: Yes, extremely.
Hammond: Colonel, there is no greater secret in this nation than the Stargate.
Jack: So we keep (Ballard) away from Level 28.
Hammond: A civilian who's spent the last 20 years of his life in a psychiatric institution?
Jack: Exactly. Who's gonna believe him if he says anything?
Hammond: Colonel, you walk a fine line.
Jack: Thank you, sir.
Fraiser: You can protest all you want Colonel, but it will be a while till you get your strength back. So relax. Ah-ah. Doctor's orders!
(Fraiser walks away)
Jack: Napoleonic power monger.
Hammond: The MALP telemetry suggests the radiation levels are still too high.
Teal'c: My symbiote provides me with a greater tolerance against the effects of radiation.
Hammond: And if that thing zaps you to wherever it sent Doctor Jackson?
Teal'c: Then I will have succeeded in locating him.
(walking into the pyramid)
Teal'c: Whoever the builders are, they would appear to be a formidable race.
Daniel: You could fit every pyramid on Earth inside this thing and still have room to spare.
Jack: Could you imagine heating this place?
Teal'c: Is someone present?
Daniel: (invisible, intangible) Yes, yes I'm here, just...don't walk through me...it's very...disconcerting.
Sam: Look at these readings, Sir! These are leptons!
Jack: ...? Get out.
Daniel: Well, there has to be some sort of radiation suit or uhm...
Jack: Hey! If you had been listening you'd know that "Nintendos" pass through everything.
Sam: Why wouldn't Daniel have told us that?
Daniel: (invisible) Oh yes, by the way, he's insane.
Jack: Rothman couldn't figure out an ash tray! The guy we need working on that thing is Daniel.
Daniel: (invisible to anyone except Nick) Repeat after me: He's standing right beside me.
Nick: He is standing right beside me.
Jack: Well, he's lost a few pounds...
Daniel: Jack, don't be an ass.
Nick: Jack, don't be an ass.
Daniel: No, no, no Nick, I'm real, you're not hallucinating!
Nick: Hallucinations always say that.
Syndication airdate: April 23, 2001.
Quetzalcoatl is the Aztec name for Feathered-Serpent, an ancient Mesoamerican god worshiped by the Aztecs, Toltec, and many Mexican and northern Central American civilizations. He is believed (by some) to be one of the four gods to have created the earth.
The Skeptic's Dictionary: There isn't a shard of evidence that these crystal skulls are mysterious in any way. What is mysterious is their continued popularity and the continued mythology as to their origins and powers.
The Skeptic's Dictionary has a somewhat better researched and plausible story behind the crystal skulls, the conclusion is that most, if not all, were actually manufactured in Germany no earlier than 1850 or so, and any tales of ancient cultures is most likely a hoax.