To what is the speaker referring when he states that his horse "must think it's queer"?
In the line, “My little horse must think it queer,” the speaker in “Stopping by Woods on a Snowy Evening” seems to be trying to put himself into his little horse’s position. From what the speaker says, the reader may gather that the speaker and his horse are traveling a known path, and that the horse is not accustomed to stopping when they are not at someone’s dwelling. Thus, the speaker believes that it must feel strange to the horse to be stopping when and where they normally would not do so.
On a more symbolic level, the speaker may be expressing his own feelings regarding the strangeness of the situation and projecting them onto his little horse. The speaker himself may not be accustomed to stopping and reflecting, especially with respect to the serious contemplation of life and death for which the “lovely, dark and deep” woods may stand. In this way, the use of the word “queer” may reflect the peculiar nature of the situation for the speaker rather than that it is merely an unusual situation for the horse.