Bookworm Riddle

Riddle

A $3$-volume set of books is on the shelf of a library, volumes $1$, $2$ and $3$ going as normal from left to right.

A bookworm starts eating from the front cover of volume $1$ and works its way through the the back cover of volume $3$.

Then it eats its way through all $3$ volumes, right?

Wrong.

Just through volume $2$.

As can be seen, when the volumes are arranged on the shelf in the specified order:

the front cover of volume $1$ abuts the back cover of volume $2$

the front cover of volume $2$ abuts the back cover of volume $3$.

So the bookworm eats through volume $2$, from the back to the front.