It could by "swarmed in line", especially if you take into account the accent. I wonder if Clarence, like many of us, may have slipped up when recording the song and actually meant to say "formed". It would make more sense...

On the other hand, it also still sounds like "sloughed" (sounds like "logged" with an "s" in front of it) if I'm expecting to hear an "L" sound at the beginning of the word. If I'm expecting to hear a "W" sound, I hear "swarmed". It's weird how the brain affects how you hear things.

Is there anything else as frustrating as trying figure out the lyrics to a song and having just one word that you can't quite decipher?