premise: A large crowd is standing around the start line. hypothesis: People are crossing a finish line.
contradiction: One scene is the start of a race where people are standing, and the other scene is the end of a race where they are crossing a finish line. You can't do both, at the same time.|contradiction: The people cannot be at the start line and finish line at the same time. Also, if they are standing around, they are not crossing the finish line.|contradiction: One is at the start, the other is at the finish.