Isn't that wild? And people say dogs don't think. How can they possible look for it later if they don't think??
They don't think the way we do, but they have highly developed systems in their brain. Their ability to make associations and remember them is unreal, and because they can use info (smells and sounds beyond our meager senses), they are sometimes better
at that than we are. Comet, for example, can tell the difference between the engine noise of Andy's Accord and the neighbor's. I cannot. I think Gus could associate the object he thought of as very powerful (tennis ball) with sights, sounds, and smells in a way that stuck with him for a long time. I wouldn't call it memory in the same exact way we have, but it's a useful, amazing kind of memory.
While I'm on the subject: because they're pack creatures, dogs have a highly developed limbic system, like ours, that allows them to love and bond like we do. Is it the same thing we have? I'd say no, since we have some other abilities, like reason, mixed in to our ability to love. Do they feel affection and bonding as strongly
as we do? The observable behavior seems to say yes, and the brain science largely agrees.
Just because the dog lags us substantially in the abstract reasoning department doesn't mean he lags in those other areas. Aren't they incredible creatures?