Dolphins found a way to con a similar system:<p>&quot;When people drop paper into the water she hides it under a rock at the bottom of the pool. The next time a trainer passes, she goes down to the rock and tears off a piece of paper to give to the trainer. After a fish reward, she goes back down, tears off another piece of paper, gets another fish, and so on.&quot;<p><a href="http:&#x2F;&#x2F;www.theguardian.com&#x2F;science&#x2F;2003&#x2F;jul&#x2F;03&#x2F;research.science" rel="nofollow">http:&#x2F;&#x2F;www.theguardian.com&#x2F;science&#x2F;2003&#x2F;jul&#x2F;03&#x2F;research.scie...</a>