The paired symphyseal tooth whorls of the Carboniferous chondrichthyan Edestus are perhaps the most enigmatic dental structures of any known vertebrate. The tooth whorls have been compared to scissors or to saw blades. It is commonly held that the tooth whorls were used in opposition, to cut prey caught between them. However, the curvature of the whorls makes such a function inefficient and therefore implausible. A symphyseal tooth of Edestus minor from the Pennsylvanian of Texas provides the first new information bearing on the function of Edestus tooth whorls in over a century. The tooth is truncated apically, and the surface of the surviving portion is worn smooth. The orientation of the abraded surface, perpendicular to the axis of the crown, suggests that the tooth whorls were used to slash prey with a vertical motion of the anterior part of the body. Such a mode of predation apparently has not been reported in any other organism, extinct or extant. In contrast to Edestus, wear to the symphyseal teeth of Helicampodus is to the sides of the crowns, probably resulting from contact with the opposing dentition. Unpublished notes of W. Langston, Jr. (1921–2013) on the interpretation of the Edestus tooth from Texas are discussed.