Perhaps it is because his head is rather large for his body, with some water having got into his brain when he was very little, so that we have to take care of him.

And though he does say very odd things, very slowly, I do not think any one of us tries harder to be good.
I remember once Mother had been trying to make us forgive each other's trespasses, and Arthur would say that you cannot _make_ yourself feel kindly to them that trespass against you; and Mother said if you make yourself do right, then at last you get to feel right; and it was very soon after this that Harry and Christopher quarrelled, and would not forgive each other's trespasses in the least, in spite of all that I could do to try and make peace between them.
Chris went off in the sulks, but after a long time I came upon him in the toy-cupboard, looking rather pale and very large-headed, and winding up his new American top, and talking to himself.
When he talks to himself he mutters, so I could only just hear what he was saying, and he said it over and over again: "_Dos first and feels afterwards_." "What are you doing, Chris ?" I asked.
"I'm getting ready my new top to give to Harry.

_Dos first and feels afterwards._" "Well," I said, "Christopher, you _are_ a good boy." "I should like to punch his head," said Chris--and he said it in just the same sing-song tone--"but I'm getting the top ready.

_Dos first and feels afterwards_." And he went on winding and muttering.
Afterwards he told me that the "feels" came sooner than he expected.
Harry wouldn't take his top, and they made up their quarrel.
Christopher is very simple, but sometimes we think he is also a little sly.

He can make very wily excuses about things he does not like.
He does not like Nurse to hold back his head and wash his face; and at last one day she let him go down-stairs with a dirty face, and then complained to Mother.