Question: This has always confused me. In the scene with the guards, which one always lies and the other always speaks the truth, Sarah asks which door leads to the castle gate then she figures out the riddle and chooses a door. However, the door she chooses, the supposedly correct choice, doesn't lead her to the entrance instead it's a trap. So did she choose the wrong door, or just the wrong direction for the hands to take her?
Answer: She did choose the right door...if she had chosen up, she would have very likely come out at the castle, but she chose down.
If you pay attention down was also the correct answer. The Goblin king was angry when he discovered she was down there "She never should have made it this far" or something similar upon finding this out. Had she chosen up she would have ended up back at the beginning.
Answer: Sarah did indeed select the right door and did ask a sensible, albeit confusing question. The reason she fell into the oubliette (and the helping hands) is because as she walked through the door she said "I think I'm getting smarter. This is a piece of cake" - saying "piece of cake" within the Labyrinth to say how easy something is brings bad luck upon those who say it. Sarah said it to Jareth and he upped the stakes (reducing her time). Hoggle said it later (in Goblin City) and then they got surrounded by Goblins.
Question: Near the end of the song "I am a dentist", is Orin saying "and a success" or "and I say sit"?
Answer: He says "and a success". He's singing about his mother telling him he'd become a successful dentist.
Answer: To add to that, the other door was supposed to lead her to certain death, and technically the oubliette wasn't exactly certain death.