Apparently, if you are training two dogs and you give one a piece of meat and the other a piece of bread as a reward, the dog got rewarded with the piece of bread may go not like it. It may get together with his friends and form a union. Okay, I made that one up.
But you can read more about the study here.
My dog does the same “shake hands” behavior, but she doesn’t do it for food. She does it so I will hold her paw and rub it, which is her favorite place to be stroked. Strange dog, I know.
