Answer by Oliver Starr:
While there's been lots written about birds, chimps and cetaceans, my own vote goes to canids. Here's one example from NOVA and another from my own personal videos:
This dog knows over 1000 words!
This wolf solves puzzles: (and steals my Apple hat as a reward) by the way, watch the little "butt hop" that keeps her tail from getting slammed in the door. In spite of never having done this before, she clearly understood the mechanics of the spring loaded closing mechanism. Smart!