Symbolism, Imagery, Allegory
The iron what?
Okay, ever see pictures of cool old medieval castles? You know those enormous metal or wooden gates that slam down to protect the entrance?
That gate is called a portcullis.
Deborah sees a portcullis come slamming down sometimes. Now, as you've probably guessed, it's not really there. But for Deborah, it seems very real.
Keeping Her Apart
The portcullis is a symbol of the separation Deborah feels between herself and the regular human world. She doesn't feel she's a part of Earth; that's why she prefers hanging out in Yr most of the time. Even when Yr gets cruel and starts punishing her, she at least feels like she's where she should be.
On top of that, although it's only mentioned a couple of times in the book, the idea that there's some kind of separation between the mentally ill and the mentally healthy pervades the story on a symbolic level.
Actually, the novel likes to point out that we can't ever really get into the head of anyone else, at least not completely. That's an idea Deborah struggles with, because it makes her feel cut off from others. Sometimes, that separateness makes her feel special and grateful to have some solitude and her own space. But sometimes it makes her excruciatingly lonely.
Why Does Deborah Need the Gate?
Let's look closely at one of the few times the portcullis is mentioned.
During one of her first sessions with Dr. Fried, Deborah lets us know this gate has been an ongoing presence in her life. When Dr. Fried tells Deborah that her parents want to come visit, Deborah "sat on the other side of the heavy twelfth-century iron portcullis that Deborah occasionally found separating them. The portcullis had been raised this time, invisible, but when the doctor had mentioned parents and a visit, Deborah heard the sudden heavy rasp, and down it clanged between them" (4.21).
Notice how the gate appears when her parents are mentioned.
At the hospital, Deborah is enjoying some freedom from her parents and their constant worry about getting her to be "normal." Never before has she had the kind of distance necessary for her to get some perspective. Being left to sort through her thoughts and feelings is scary and liberating all at the same time.
So when she hears the word "parents," that door comes slamming down. It's one more layer Deborah can throw up to protect her secret self.