Journal of Comparative Psychology (2010) - Comment
pubmed: 20476822  doi: 10.1037/a0018083  issn: 1939-2087  issn: 0735-7036 

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Catherine M. Bohn-Gettler, Anthony D. Pellegrini, Danielle Dupuis, Meghan Hickey, Yuefeng Hou, Cary Roseth, David Solberg