With all his treatment, James has gotten interested in the different blood cells and how they work. His favourites are the macrophages which are white blood cells that do a cunning trick of growing arms to swallow bacteria etc (see an amazing animation and a time-lapse video).
The other week, he was sleep-talking and was obviously dreaming - he said "My brain can control the macrophage" - and went straight back to sleep
Then on Monday I was reading a book from the library about the Body (again fascinating to him) and there was a section explaining how in the Spleen, macrophages take apart old red blood cells so there parts can be recycled.
We finished reading and he said to me, "Daddy, I'm a macrophage and you're a red blood cell. When you're old and can't work any more, I'm going to tear you to pieces in the spleen"