Very interesting, thanks, Ed.
I also use a distinct hand/arm signal for all Puff's verbal commands, e.g., ours are: "sit" = bang fist once on imaginary table, "come" = slap my chest with the palm of my hand, "down" = point finger at the ground, "speak" = imitate an opening duck bill with thumb & palm, etc.
I think it was last year, someone published an experiment on a remarkable dog in Europe that knew the names of over 400 objects. When told to go to another room and bring back the __Q__ , the dog would always bring back the correct object.
IIRC, they then placed a new object that the dog had never been trained on among the other familiar ones and asked it to fetch a ==X== and the dog brought it back apparently because since it wasn't familiar with the name of that object this new object must be the right one.
I think that may be quite a bit smarter than the average 2 year old -- certainly smarter than Puff.