Let's dive into another brief flashback, from when Christopher first started going to school:
His teacher sits down with him and takes out a tube of Smarties (not the American kind!).
She asks him what he thinks is inside the tube. Um, Smarties?
But when she turns the tube upside-down, a small red pencil comes out. Whoa.
Then she asks him what Christopher's mother would think was in the tube if she came in the room right now. Christopher says that she would think there was a pencil inside.
In the present, he explains that this is because, when he was younger, he "didn't understand about other people having minds" (164.8).
One more quick dip into the flashback: the teacher explains to Christopher's parents that he would always have difficulty with this sort of thinking.
Okay, back to the present. That kind of stuff doesn't trip him up anymore. Now he thinks about it like a puzzle, trying to figure out what other people know.
Christopher spends some time comparing human minds to computers, and human minds to animal minds: he says that most people think humans are different from computers because humans have emotions, but really "feelings are just having a picture on the screen in your head of what is going to happen tomorrow or next year, or what might have happened instead of what did happen, and if it is a happy picture they smile and if it is a sad picture they cry" (163.20).