A plate lifter or plate wobbler is a novelty item[1] consisting of a tube with a small flat[2] bladder on one end and a bulb on the other.[3] The bladder is to be placed under a plate; inflating it will make the plate wobble.[4] This fake demonstration of psychokinesis[2] is intended to provoke surprise and merriment.[5][6]
A free plate wobbler was included with the first issue of the British comic magazine Monster Fun and promoted as a "monster mirth maker".[1]
Get a 'plate lifter' at your local joke/novelty shop. This is a long tube with a little bladder on one end and a bulb on the other. The original joke was to hide the bladder under the table cloth under plates to make them jump up and down when the bulb was squeezed.