As we were listening, I became particularly interested in the words "Sycorax" and "patagon," especially when Professor Brewer mentioned them after the song was over, so I looked them up. While I realize that Wikipedia typically is not a credible source in the academic world, I think I can use its general definitions of these words without risking a fiasco. That said, Sycorax has several meanings/implications/allusions. First, it refers to two episodes of the British Doctor Who series. In one episode, a fictional race of aliens invades, and that race is called the Sycorax. In a later episode, the Doctor travels to Shakespeare's time and, in Shakespeare's presence, mentions the alien race from the abovementioned episode; in this Dr. Who version of history, Shakespeare likes the word "Sycorax" and decides to use the word in one of his plays. This takes us to the next definition: in fact, Sycorax IS the name of a character mentioned in Shakespeare's The Tempest. This is the earliest instance of the word that I can find, but I thought it would be interesting to tie it into the above definition first. Finally, Shakespeare's fictional Sycorax was honored with the discovery of one of Uranus' moons, which is now called...Sycorax! As for "patagon," I found that it simply refers to a mythical race of people who are double the size of regular humans.
Although there are many potential reason's for The Decemberists' use of "Sycorax," it is clear that BOTH of the words in question are references/hommages to something that is (1) fictional, (2) perhaps larger than life, (3) mysterious, and (4) other-worldly. With this context in mind, we get a sense of danger from the lyrics, as a child, asleep in its cradle, is being watched by both "Sycorax and patagon" (from different vantage points, which is what "parallax" means, for those of you who don't know the word). As such, I can only picture Sycorax as the alien race mentioned in Dr. Who. It just makes the best sense. The scene therefore can be represented by the following: a sleeping child being watched by an alien, from one point, and a mythical giant, from another point. This also accounts for the "foretold rumbling" in the next line of the lyrics, as the giant would no doubt produce a rumbling as he/she walked the Earth. Usually when we think of aliens and giants, at least in my experience, we think of them as sinister or potentially harmful, at least at first, and because of this, the song seems eerie. The dark tone of the song can also be seen in the second and third sections of the song, which speak of "death," an "ugly" person, "drowning," and "dimes laid on your eyes," to name a few examples. I am particularly interested in the line about dimes, which closes the song. The dimes seem to refer to the coins that one would put on the eyes of the dead as a tip for Charon, the driver of the underworld's ferry/boat. It also ties into a main theme in the song/poem: eyes/seeing/sight. Some examples of this theme at work include the lines "Come and see" and "With this bare waking eye."
As a final note, I would be interested in knowing the actual reason that The Decemberists used "Sycorax," as this knowledge might shed some more light on what the word means to the lyrics/poem. Perhaps there is ANOTHER definition of the words, one that I have missed. Does anyone know if there is?