In the episode The Case of the Fanciful Frail
when real money is burned, it turns into "stage" money.
The money in the box appears to be legal United States currency; i.e. "real money".
As the money is dumped into what appears to be an empty ice bucket,
the money has been magically changed from "real" money to "stage" money.
The shadowy stranger sets fire to the money in the ice bucket.