What does 1 Samuel 6:4 mean?

The Philistines asked, 'What kind of guilt offering should we send?' The priests replied, 'Five gold tumors and five gold rats, one for each Philistine ruler, because the same plague hit all of you and your rulers.' 1 Samuel 6:4 - Modern Text Bible

(The priests suggest making gold models of the tumors and rats, representing the plagues, as a symbolic offering.)