Sylvia: Dad? What is that thing the Master gave Lyra? What did he say it could do?
Me: The Alethiometer you mean? He said it was a machine that would tell her the truth.
Sylvia: ...I think it's going to tell her that she's a Gobbler. He knows it and he wants it to tell her.
Me: Hm, that sounds like it could be...
(A minute later) If he knows though, why doesn't he just tell her?
Sylvia: Because she would probably just refuse.