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. 2021 Nov 18;25(3):597–603. doi: 10.1007/s10071-021-01582-5

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© The Author(s) 2021

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Fig. 1 — a Test apparatus consisted of two outer solvable compartments and one middle unsolvable compartment. The apparatus was placed b in the middle back of the test arena with the owner and experimenter standing in each front corner of the marquee