It's an attraction I had at the place I ran back in Gravity Falls, the Mystery Shack! It was a big burlap sack with a question mark on it, and I'd show it to the crowd and go--

[And he puts on his best salesman voice, as though that will make it more believable.]

"You put your money in the sack, and it magically disappears!"

People ate it up like candy, and I made a killing!