Cleave gag
From Wipipedia
A more effective variant of the OTM gag is called the cleave gag. Instead of being tied over the bottom's mouth, the scarf or cloth is pulled between his or her teeth. While a thin material isn't very effective, a thick scarf can be used to hold his or her mouth open, and the tighter that gag is tied the better it works. Occasionally, a knot is tied in the centre of the gag so it works more like a ball gag.
