This chapter is about the skills that Christopher is master of. So Christopher is able to search his mind for persons, metaphors, statements etc. He can order these things like a movie and as a result he is good at remembering those things. You can imagine this working like a video recorder.
The chapter gives you example for this. So Christopher is with his parents on holiday in Cornwall. Cornwall is a region in southern England and there is the sea, of course. Then his mum takes a bath in the sea and she wants Christopher to come in and to swim with her. As she begains to dive he begins to cry because Christopher thaught that there were sharks but his mother tell him there aren´t any sharks and then the situation is cleared.
It`s really impressive that Christopher can search is mind and that he can remember things and I think that this restores to the AS which Christopher has.