Knock on the Mini Monster Box and a little monster peeks out. The lid opens and closes at random speeds and stays open for varying lengths of time.

Electronics maker Øyvind Nydal Dahl built it for his young daughter. A microphone detects the knock, while an Arduino and servo motor move the lid.

A child was frightened of the family's robot vacuum and would turn it off whenever it started moving. To help the two get along, the maker fitted the vacuum with a motorized tail, inspired by the child's love of cats.

A servo pulls fishing line to bend the tail, with randomized speed and angles to make it feel more lifelike. The tail alone did not hold the child's attention for long, so the maker also added a fluffy cover. The child began petting the vacuum and offering it stuffed animals.

To give in-game death more physical consequence, maker Hori built a system where dying in Super Mario Bros. triggers a basin to fall from above the player's head. The setup listens for Mario's death music, then activates a servo that releases the basin. During testing, microphone noise caused a false detection and dropped the basin even though Mario was still alive. A machine designed to increase immersion accidentally introduced its own real-world version of an unfair game event.