OK, mrz, sure. But doesn't this partially depend on the size of the book? Dr Suess books are too long to learn by heart for small children, (probably most adults too) You can memorise the gist of the books, sure, but not every line. In fact my daughter does exactly that and she "reads"
I do not like them with a fox. I do not like them in a box.
When what it actually says is
I would not like them with a fox. I would not like them in a box.
And I look at her sideways and say, is that really what it says? Children may think they know the text. But it doesn't mean that they do.
And she says, no. Then she reads it properly. Other times she reads fantastically up to about page 40. I mean turns the pages herself, scans and reads the lines and I sit about a foot away from her. She reads perfectly. But at about page 40 she starts reading nonsense. And the text is pretty uniform throughout. So I stop her and we start sounding out each word in turn, words she's read forty pages of perfectly. And she's still squirming about in the chair and talking nonsense.
She's just tired. So I put the book away and turn on CBeebees.