In the recording, a voice whispered, barely audible over the screech of the steel wheels: "It doesn't feel like metal to me. It feels like skin."

The train plunged into a tunnel, and the recording cut to static.

He pressed play again. The sound of the train shifted. The mechanical grinding turned into a sound like teeth gnashing against bone. The "breather" began to sob, but the sobs turned into a rhythmic, mechanical whistle.

"I'm not riding it," the voice on the recording gasped, now sounding distorted, as if its throat were made of copper piping. "It’s riding me."