From the November 3, 1921 Skidmore News (Skidmore, Missouri), page 1:
Skidmore High School will give a “Shadow Box Supper” Friday night, November 18. It is thought that this is a new stunt in this locality and will need some explanation. A large sheet is stretched across the front of the room and lights are so arranged that when anyone steps behind the sheet their shadow is shown plainly.
The girls go behind the sheet and the crowd bids on the shadow. The highest bidder gets the girl who made the shadow, and the girl furnishes a box.
There will be further notice of the supper in next week’s paper. Every one come. Girls, bring a box, and boys, come and bid.