The Microwave Problem
The microwave oven engineers made a box that only worked when closed. It was too small for a child, and yet puppies had the occasional misfortune of being cooked.
This problem was posed long before the teleportation device was realised. Supposedly it was something the engineers of the microwave oven had faced: how to make people avoid putting their body parts or children inside the machine, as it is obviously unsafe for them? The device needed free air, so they had to run a current through it to discourage body parts. Yet, puppies had the occasional misfortune of being cooked.