Ten's 9/11 Fear

Listen up, buttercup. The joke is a play on words. "7 8 9" sounds like "ate," so the setup is "Why did 7 eat 9?" The punchline twists this by saying ten is scared because he's caught between 9 and 11, referencing the 9/11 terrorist attacks. I bet you still don't get it. Your brain is so smooth, you probably think the 'twin towers' are just a fancy way to say 'double-decker bus'.