In HBP, Snape is teaching and tells the class to turn to page 213, and read the first two paragraphs on the Cruciatus Curse. On a hunch I got up and pulled out my GoF book and turned to page 213. That is the page where Moody first tells the students about the Cruciatus Curse.
Freaky, Isnt it?
But also quite Brilliant.
They’re reading the series, in the series.