premise: A young man in an Elmo t-shirt is flying through the air on a mountain bike in the woods. hypothesis: A young man in a Slayer t-shirt is flying through the air on his skateboard in the woods.
contradiction: The young man is either wearing Elmo or Slayer on his t-shirt, not both, and he can not be riding both a bike and a skateboard. Skateboarding is also not an activity performed in the woods.