Manuel Leal and Brian Powell at Duke University in Durham, North Carolina, presented six Puerto Rican Anolis evermanni lizards with two wells (pictured), one of which contained a fly larva reward and was associated with a plain blue disc. After a habituation period, the creatures were challenged to dislodge the blue disc covering the well with the reward. Four of the six lizards repeatedly solved this problem by either biting or shoving the cap aside to reveal the treat, and chose the blue disc over differently coloured discs. When the reward was placed under a new disc colour, two lizards were able to reverse their choice.