Representing tools: how two non-human primate species distinguish between the functionally relevant and irrelevant features of a tool
Animal Cognition (2003) - Comment
pubmed: 12736800  doi: 10.1007/s10071-003-0171-1  issn: 1435-9448  issn: 1435-9456 

Laurie R. Santos, Cory T. Miller, Marc D. Hauser