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The number of nuts cracked open by the subjects in each session, including the first test session and the 10 sessions at the beginning of the follow-up training session that was originally reported in Hayashi et al. [23]. A chimpanzee, Pan, succeeded in cracking nuts from the first test session. Although a chimpanzee, Chloe, failed in the first test session, she succeeded in the first follow-up session conducted after a hiatus of approximately 4 years.
