Rock-paper-scissors game

Chimpanzee Chloe doing the rock-paper-scissors task.
In each trial, there were two choice alternatives (three kinds of pairs:
"paper-rock", "rock"-"scissors", "scissors"-"paper"). The open chimpanzee
hand represents "paper"; the chimpanzee fist represents "rock"; and the
second and the third fingers forming a "V" shape represents "scissors".
Chimpanzees were trained to choose the stronger one according to the game
rule ("paper" beats "rock", "rock" beats "scissors", "scissors" beats
"paper"). The three pairs appeared randomly in a session. When they made
the correct choice, a food reward would be provided.
Researchers in Primate Research Institute, Kyoto University found that
chimpanzees are able to complete the task and to learn the circular
relationship of paper, rock, and scissors in this game.
Jie Gao, Yanjie Su, Masaki Tomonaga, Tetsuro Matsuzawa(2017)
Learning the rules of the rock-paper-scissors game: chimpanzees versus children.
Credit: Primate Research Institute, Kyoto University