premise: Two men, sitting on ambulance motorcycles, are talking to each other. hypothesis: Two men, standing by an ambulance motorcycles, are yelling at each other.
contradiction: When people are sitting on motorcycles and they are talking, they are communicating in a peaceful manner, and their backsides are on the seat of the motorcycle; they cannot at the same time be standing by their motorcycles while they are yelling as that is an upright position and a different tone of voice and volume.