What kind of understanding is there between the horse and the speaker of the poem?

In "Stopping by Woods on a Snowy Evening," the man and his horse seem to have an understanding that they will perform their duties with no lollygagging. Thus when the man stops to watch the woods fill up with snow, pausing from his journey to merely take in his surroundings, the horse "gives his harness bells a shake." The speaker in the poem imagines that the horse "must think it queer/To stop without a farmhouse near." This suggests that the horse's normal routine, and therefore the man's as well, is to go from one farmhouse to another. The man has "promises to keep," so his life is filled with obligations, and he doesn't take time to stop and smell the roses. The understanding between the man and his horse is that they will keep moving until their mission is accomplished. They don't take time to rest or to do something as aimless as stopping during a snowfall to listen to the wind and enjoy the scenery or to contemplate any other matters. They live under modern life's tyranny of the urgent. Daily demands eat up all their time and energy. The man evidently doesn't slow down enough to contemplate what is really important in life or even just to have fun. His horse therefore shakes his harness as if to hurry the man along, as if to point out the man's "mistake" or veering from their usual practices. The horse is used to a life of duty and obligation, a lifestyle it shares with its master, except for the few minutes on this snowy evening.

There seems to be a pretty deep level of understanding between the speaker of the poem and his horse.  It's likely that they spend so much time together, typically in the same familiar places, that they both know the routine so well that they really have to communicate relatively little in order to do what they need to do.  But now, in this poem, the speaker says, "My little horse must think it queer / To stop without a farmhouse near" (lines 5-6).  They have made a stop that is off their beaten path, in the woods, not where they typically stop.  The narrator knows his horse so well that he anticipates the horse's response to straying from their routine.  Then, when the horse shakes his head, the narrator attributes this to the horse's confusion about the unexpected stop.  The narrator says, "He gives his harness bells a shake / To ask if there is some mistake."  The speaker somewhat personifies the horse, suggesting that he is asking the speaker a question, and so this seems to indicate a high level of understanding, or at least a close bond, between narrator and horse.