This is the first time a peacock's cry is mentioned. It feels out of place and disruptive, but this is the way Stevens brings reality and imagination together in this poem. Up to this point the reader may be confused as to where exactly the speaker is, but none of that really matters. What does matter is that a sudden irksome memory has been summoned by the thought of a hemlock tree. I say that it is an irksome, or troubling thought, because the cry of a peacock is not harmonious or appealing to the human ear. To give you an idea here is a video of a peacocks cry.