What does the description of the horse tell us about the speaker?
It seems like the speaker might be just a little lonely based on the way he talks about his horse. He attributes a great deal of understanding to the horse, assuming that the horse is thinking that it is odd for them to be making an unscheduled stop in the woods, nowhere near a farmhouse, and totally alone in the night. Further, when the horse shakes its head, the speaker assumes that the horse is purposely jingling his harness bells in order to question him about the reason for the stop and if he has made some error. Other than the horse, the speaker is alone, and he says that he still has "miles to go" before he can rest. This sounds like a bit of a lonely road he travels, and so his descriptions of the horse make it seem as though he thinks of the horse almost as another person in order to be less lonely.