Scientists have reported tool use in many species including chimps (they use twigs to fish termites out of termite mounds), crows (one crow filled a cup up with water and poured it over its food to make it more palatable) and rooks (in one study, they bent a wire to fish a worm out of tube). What about dogs?
Is this dog using the raft as a tool? To answer that, let’s look at a few definitions of tool use:
[Tool use is] the use of an external object as a functional extension of mouth or beak, hand or claw, in the attainment of an immediate goal (van Lawick-Goodall 1970, p. 195).
Hmmm, the dog doesn’t exactly use the raft as an extension of its mouth or paw so according to this (out-dated) definition, the dog is not using the raft as a tool.
Tool-using involves the manipulation of an inanimate object, not internally manufactured, with the effect of improving the animal’s efficiency in altering the form or position of some separate object (Alcock 1972, p. 464).
The raft is an inanimate object. The dog manipulated the raft and that manipulation improved the dog’s efficiency in altering the position of itself (not the ball). This definition comes so close…so if the dog pushed the raft towards the ball so that the ball floated closer to the edge–that would be tool use? Using the raft as a boat was certainly more efficient.
Thus tool use is the external employment of an unattached environmental object to alter more efficiently the form, position, or condition of another object, another organism, or the user itself when the user holds or carries the tool during or just prior to use and is responsible for the proper and effective orientation of the tool (Beck 1980, p.10).
Again, the user must hold or carry the tool. Does that mean that a car is not a tool?
Tool use is the exertion of control over a freely manipulable external object (the tool) with the goal of  altering the physical properties of another object, substance, surface, or medium (the target, which may be the tool user or another organism) via a dynamic mechanical interaction, or  mediating the flow of information between the tool user and the environment or other organisms in the environment (St. Amant and Horton 2007, p.10).
Aha! This definition says that the tool user can be the target. The dog alters its own physical properties by riding the raft. Therefore, the dog uses the raft as a tool to fetch the ball, right?
What do you think?