The Shawshank Edit Meaning

1.

A classic revenge technique in which the offended party hollows-out a space in a hardcover book and then deposits his bowel movement in said book. Upon closing the book, he places in on the bookshelf or desk of the offending party, where it festers undiscovered for weeks until the smell finally subsides.

Your roommate sleeps with your girlfriend while you're on a business trip, you need a non-violent, yet maddening way to re-pay his disloyalty. Hence, the Shawshank.