“…Enrichment with toys has been previously found to positively affect both physiological (i.e., diminution of cortisol level) and behavioral responses (i.e., increase of normal behaviors) in nonhuman primates (Boinski, Swing, Gross, & Davis, ). Delays in receiving food as well as teasing were used to induce negative emotional states, where some level of frustration most likely was experienced during the waiting (Miller & Karniol, ; Mischel, Ebbesen, & Zeiss, ), which may have even escalated into anger (Henna, Zilberman, Gentil, & Gorenstein, ). The toy, tickling, food delay, and teasing conditions were preceded by a neutral baseline, where each subject was in a relaxed state.…”