Corner Market
The Futility Closet shares a classic Martin Gardner puzzle.
http://www.futilitycloset.com/2014/04/15/corner-market-2/
I think this is a little more subtle than the more common triangle paradox. What do you think?
gifs of this at my tumblr. http://mathhombre.tumblr.com/post/82787608599/infinite-gold-the-futility-closet-shares-a