While looking at William Golding's The Spire on Amazon, I noticed a tiny link right below the title and author that said SIPs: corkscrew stair. That's enigmatic enough for me, so I clicked. It turns out that Amazon is now displaying SIPs—Statistically Improbable Phrases—based on their "Search Inside the Book" feature. There's an explanation, but basically SIPs are phrases that appear a lot in a particular book and hardly at all in other books. Pretty cool.