Figure 2. Experiment 2 testing procedure and results.

A. Depictions of the testing procedure. (1) displaying the choice options to the monkey, with the experimenter on the left (with backpack) presenting the apple and cucumber slices, and the experimenter on the right (backpack not seen in this view), presenting the apple slice alone; (2) the monkey making its choice. B. Experimental results for all three test conditions. (1) one cucumber slice alone; (2) a cucumber slice versus an apple slice; (3) an apple and cucumber slice versus an apple slice alone. Data were analyzed using two-tailed Binomial tests: * = P<0.05; ** = P<0.01; **** = P<0.0001.