What does the owl eyed man find extraordinary about the books in Gatsby's library?

The books are real books, not just the front cover for show.

However, back in 1920's when a book was binded the pages were still stuck together, so when somebody has read the book they would have to tear the pages apart (therefore leaving jagged edges)

The owl-eyed man notices that the books have not been read at all, this is the irony in the books, they are as good for show only.

This is also a way Gatsby shows of his wealth, to win back Daisy.

"Absolutely real -have pages and everything......Knew when to stop too, -didn't cut the pages...."pg 51-52