Quote 19
I sat on the bed for a long time looking at the floor. Then I heard Toby scratching in his cage. I looked up and saw him staring through the bars at me. (167.29)
Here's another powerful image, as the rat's physical isolation in the cage parallels Christopher's emotional isolation. We might even compare Toby's scratching to Christopher's uneasy processing of his realization about his mother being alive. Deep.
Quote 20
I do not like people shouting at me. It makes me scared that they are going to hit me or touch me and I do not know what is going to happen. (5.5)
The first part of this is pretty inarguable – none of us wants to be shouted at or hit, right? But then Christopher takes a pretty big leap, suggesting that he needs to <em>always</em> know what's going to happen, and what everyone around him is going to do next. Now that's a recipe for disaster.
Quote 21
Then the police arrived. I like the police. They have uniforms and numbers and you know what they are meant to be doing. (11.1)
This naturally implies that Christopher has difficulty with most other people because, well, he doesn't know what "they are meant to be doing," and that makes him nervous.