Yuko Hattori1, Masaki Tomonaga2. 1. Center for International Collaboration and Advanced Studies in Primatology, Primate Research Institute, Kyoto University, Inuyama 484-8506, Japan; yuko.hattori@gmail.com. 2. Language and Intelligence Section, Primate Research Institute, Kyoto University, Inuyama 484-8506, Japan.