What does Rudy find in the dirt?

Rudy finds a coin in the dirt.

It was sitting half rotten in some dirt, on the washing and ironing route. A solitary corroded coin.
“Take a look at that!”
Rudy swooped on it. The excitement almost stung as they rushed back to Frau Diller’s, not even considering that a single pfennig might not be the right price. They burst through the door and stood in front of the Aryan shopkeeper, who regarded them with contempt.