Apparently, "used book smell" wasn't quite good enough to describe that unique smell we literary lovers all adore. In fact, it wasn't even good enough to know the smell came from old books; these guys (above) decided they'd find out exactly what causes it.
In the enlightening video above, you'll find out that scientists have officially classified the smell as: "A combination of grassy notes with a tang of acids and a hint of vanilla over an underlying mustiness."
Well. This just sounds kind of fun to me. So: how would YOU describe the smell of old books?