Fare la scarpetta

Now here is a cool expression.

"Fare la scarpetta" means to clean your plate during a meal. Usually, Italians do so with a piece of bread, making sure to sop up all the olive oil and other juices of a given meal.

Literally, of course, it means "do the little shoe." Why? I don't know.

C'è qualcuno che ci può spiegare l'origine della frase 'fare la scarpetta'? Ne sarei grata.

(The phrase comes to us, once again, from "The Streetwise Italian Dictionary/Thesaurus.")