On a ride awhile ago, a dog (looked like a pit mix of some kind) came out and essentially raced me for a block or so. It ran parallel to me, giving everything it had. Just before giving up, it managed to look over at me and bark once. Other than that, it was putting all its energy into the run. I could tell it was a happy sort of chase, and just maintained my speed, which was low 20's. Fun experience for both of us.