People get all excited when animals use tools [1, 2, 3] to accomplish something.  But, what if an animal uses a human to accomplish something?

Dogs scratch at the back door to be let out, for instance.  Sure, in a sense, we train the dog to do this.  But once the dog has made the association between scratch and outside, then the dog can start using that scratch to induce his humans to open the door.  We are the tools that the dog uses to open the door.

This idea is similar to the “Machiavellian Intelligence Hypothesis [4] which states that we evolved intelligence to take advantage of each other.  [Though it should be noted that people cooperate with each other, even at a cost to themselves [5], so the emphasis on competitive behavior may be just a scientific fad.]