A late 16th century mouth gag. A similar instrument, Paré’s mouth gag C 1570 from the Royal College of Surgeons of England is shown on page 212 of Elizabeth Bennion’s “Antique Medical Instruments”.
The thread of the screw is reversed at its centre so that turning the fixed wing nuts opens or closes both handles at the same time. Having the fulcrum so close to the blades allowed considerable force to be applied through this mechanism. It would have been used to pry open the mouths of patients with lockjaw who might not otherwise be fed and would also have been used as a dental mouth gag. Note the heart shaped makers mark on one of the handle