I flew CLT - LAS last year in Coach with a large black labrador retriever under the seat in front and to the right of me. It was a service dog for the man sitting next to me on this completely full flight. I admit that I cringed when I first saw the dog sitting down, but the dog was an incredible seatmate. It made not a single sound on the ~4 hour flight and never got up or even moved until we arrived. The dog's owner, a blind man on the way to a Lions Club meeting, also turned out to be a really nice guy. I would gladly fly with both of them any time!