“…de Blois & Novak, 1994;Natale, 1989;Neiworth et al, 2003], one gibbon [Fedor et al, 2008], domestic cats and dogs [see Dumas, 1987 andGoulet, 1998 for reviews], a few lemur species [Deppe et al, 2009], and bottlenose dolphins [Jaakkola et al, 2010, but see discussion regarding a training procedure implemented, which might have contributed to success]. Furthermore, research indicates that single visible displacements are easier to solve than double visible displacements [e.g.…”