Chimpanzee (Pan troglodytes) intentional communication is not contingent upon food
Animal Cognition (2005) - Comment
pubmed: 15742162  doi: 10.1007/s10071-005-0253-3  issn: 1435-9448  issn: 1435-9456 

Jamie L. Russell, Stephanie Braccini, Nicole Buehler, Michael J. Kachin, Steven J. Schapiro, William D. Hopkins