Riddle: A man was found dead next to a 13 story building. The police say it was a suicide, but you say it was a homicide (someone killed him). To prove this, you go to each floor on the building, open the window, and toss a penny out. You do this to each floor until you reach the 13th floor, open the window, and toss a penny out. How does this prove it wasn't a suicide?
Answer: If the man committed suicide, he would've left the window open and you wouldn't have had to open it.