Check out this nifty and fun puzzle using lines, or matchsticks, to change the direction of the swimming fish by moving just three lines or matches.
With a bass, or a pike, or trout, or any other fish, you need start out with eight lines or matches. Then ask yourself, "how can I move just three lines to make the fish swim in the other direction?"
This puzzle is simple, yet tons of fun, until you get bored of it. Then go find yourself another perplexing game to play.