A thought I had:
In Narnia, people often address humans as 'Son of Adam' or 'Daughter of Eve'.
In The Silver Chair, this confuses Jill, as she comes from a non-religious background and hasn't heard of Adam and Eve.
However, while Aslan himself often uses 'Son of Adam' or 'Daughter of Eve', he never addresses Jill this way. He knows her, and where she's coming from, and always calls her simply 'Human Child'.
I like that.