Stanley loved fishing and also loved boasting about how an amazing person he is. One day he went into a bar after fishing, and started telling people in the bar about something that just happened. "So I was fishing by the waters, really nice breeze, and suddenly there was this person who creeped from behind and wanted to stab me in the stomach. Because I'm so good in Kung Fu, I turned back and WHAM! I slapped him in the face!" Everyone enjoyed the rest of the story when one person asked him: "You're lying, Stan, are you?" How did the man knew that Stanley was lying?
How can the man stab Stanley in the stomach if he's creeping up from BEHIND?