Photo: science Museum London
That's the "Scold's Bridle," a gruesome mask used as punishment for "rude, clamorous woman," who are considered to be spending too much gossiping or quarreling in the Medieval times. It came complete with a bell on top, no less:
Time spent in the bridle was normally allocated as a punishment by a local magistrate. The custom developed in Britain in the 1500s, and spread to some other European countries, including Germany. When wearing the mask it was impossible to speak. This example has a bell on top to draw even more attention to the wearer, increasing their humiliation. It was used until the early 1800s as a punishment in workhouses.
From Science Museum's Brought to Life: Exploring the History of Medicine: Link