Which he does pretty quickly. He starts yelling at her, asking how she could know that the little boxes would make him angry. She calmly opens her eyes and welcomes him as her thief. In the TARDIS, Amy is fretting because the Doctor isn't trusting her and is getting emotional, which means things are about to go very bad. Which is when Rory notices the sickly green glow coming in through the windows on the side of the TARDIS, and they realize that she is very, very right. Commercials.
The Doctor is asking Idris who she is. Idris: "Do you really not know me, just because they put me in here?" Doctor: "They said you were dangerous." Idris: "Not the cage, stupid. In here." And with that, she gestures to her own face. She can't think of the word to tell him who she is, so she describes what she does. "We travel. I go [insert TARDIS sound here]." He thinks she's mad, but she seems pretty confident in who she is. "Type 40 TARDIS. I was already a museum piece when you were young. But the first time you touched my console, you said..." Doctor: "I said you were the most beautiful thing I'd ever known." Idris: "And then you stole me. And I stole you." He tells her that he borrowed her, and she points out that borrowing requires the intention to eventually return what you take. And she never had any plan on giving him back. He finally believes her. With a start, she realizes that they've reached the time when he opens her cage. And he pulls out his screwdriver and does just that. Idris: "Are all people like this?" Doctor: "Like what?" Mad and with giant hair? No, that's just you and Helena Bonham Carter. Or, actually, she answers, "So much bigger on the inside." There's some terribly big, complicated, sad word she wants to use to describe herself, but she just can't put her finger on it. The Doctor wants to know why someone would possibly want to pull the soul out of a TARDIS and stick it in a puny human brain. She tells him that House eats TARDISes, but she doesn't really know what that means -- it's just something she heard the Doctor say in the future. And then she asks, "What are fish fingers?" Doctor: "When do I say that?" Idris: "Any second." And then the Doctor realizes that House eats TARDISes, because they represent lovely processed rift energy, just like his precious processed fish fingers. Idris excitedly tells the Doctor that by pulling the matrix out of a TARDIS, House is free to move in and eat all the energy. And then she realizes that she was just repeating what he was about to say, thereby making it unnecessary for him to say it.