The cardboard box needs to be large enough to hold one of the players and various props. "Load" it and push it on stage, where a narrator explains that this marvelous machine has been invented by tonight's guest, Professor…, who will demonstrate its tremendous powers. He introduces the professor, who enters carrying a bag of his props.
The professor explains he has invented a wonderful machine that makes things grow. He proceeds to demonstrate. He pulls a small piece of paper from his sack, pushes buttons, etc., and throws in the piece of paper (sound effects, flashing lights). The player inside throws out a paperback book. The demonstration continues with small ball in, large ball out; piece of string in, hunk of rope out; etc. Finally, the professor throws in a baby doll. The player inside jumps out in baby clothes, cries "Daddy!", and chases him off stage.