>>Nor can I think of any other absolutely-accepted difference.
Can you?<<
There is one other difference. As of this moment, there is no example of an
animal making a tool with which he makes a second tool to perform a third
purpose. A look at the list of tool use in Kathy D. Schick and Nicholas Toth,
Making Silent Stones Speak, (New York: Simon and Schuster, 1993), p. 53,54,
reveals two interesting facts. Only Chmpanzee and man modify objects for use
as a tool and but chimps do not use their tools for anything but the
immediate purpose.
This of course may change but it is the case today.
glenn