It's been over 20 years since I saw the nudger, from memory it was on BA 747-200s that I saw it.
It was easy to demonstrate you simply activated the stall test on the overhead panel, the stick shaker(s) would activate and after a few seconds you would see the control column drive forward, once the stall test switch was released the shaker(s) stopped and the column would return to neutral.
* Can't remember if BA used single stick shakers or dual.