It's an old one, this joke simply gets people thinking, laughing and talking. I own a hard cover book on the Principals of Training for Competency; it's printed upside down and read backwards from the end of the book.

LOL and reminds me of a day trip into Seattle. Filling up my car, went to pay and saw bullet holes in the pay booth. Clerk had a sign on window; Don't know when this happened. No-one was hurt. I wasn't on duty. Have a nice day.