"When we force ourselves to go topsy-turvy, we can see anew what is on the page," (p. 49).
She suggests taking a single chapter and re-reading the whole thing while changing the gender of the characters, or the point of view, or leaving out all the modifiers, or counting how many times you've used each sense for events you've related. It's to help you see where you've repeated yourself, among other things.
She notes also that turning a prose paragraph into lines of poetry (just breaking the lines, not rhyming or anything) can help you identify where you've overwritten. Turning poetry into prose can help you see if you've been too cryptic.