He had torn off the assassin's mask revealing a lipless mouth cut wide across the man's cheeks filled with razor sharp teeth.
Under his mask, the assassin hid an unpleasant looking face. 
mnli hypothesis: Under his mask, the assassin hid an unpleasant looking face.  premise: He had torn off the assassin's mask revealing a lipless mouth cut wide across the man's cheeks filled with razor sharp teeth.