People in crowds can get hurt when trying to force their way through doorways, eg to escape from a burning building.
Today’s invention is a doorway which reacts to the pressure of a crowd.
In the diagram on the left, the people are jammed in the doorway.
In the right hand image, the door and sidewalls have begun to oscillate slowly backwards and forwards over a small amplitude, thus jiggling the people free from the jam, like sand in an egg timer.
An electric motor would first expand the room, freeing a small number of people, before returning to the normal configuration and repeating the process.
(My eldest daughter has just pointed out that the oscillation might instead be of the door jambs alone, in the plane of the wall).