He jammed on the riff a little bit, and "it was just one of those things that happened magically. ... A lot of times I'll sit down and the shit will just drop into my hands and I don't even think about it.
He experimented with the riff a bit, and "it was one of those spontaneous occurrences that felt inevitable. ... Frequently, when I'm composing, the ideas come to me unexpectedly, and I don't even realize I'm doing it.