"Fire Fire" was The Spine’s way of telling the other robots what happened in the space shuttle explosion. The ship’s black box (a recording device installed in most airplanes and ships) recorded the whole accident, and was one of the few pieces of the ship to be recovered. The Spine downloaded the data from this black box, and he couldn’t bring himself to tell the others what he saw. In order to make it easier to explain what happened, he wrote the "Fire Fire" and sang it to the others. That is why he is the only one to be heard singing and playing in the original recording.