The subway was the heartbeat underneath the Lower East Side. You did not hear it. You felt it. The F train passed under Delancey Street and the building shook and the coffee in your cup made a small circle and the small circle was the train saying hello from forty feet below.

The rumble came every four minutes during rush hour and every twelve minutes after midnight. You could set your clock by the rumble except nobody did because everybody had a clock. But the building knew the schedule. The building had been memorizing the schedule since 1936 when they dug the tunnel. Ninety years of trains underneath the same dirt and the building had learned the rhythm the way your heart learns to beat. Not by choice. By repetition.

The people on the first floor felt the rumble in their feet. The people on the second floor felt it in their knees. The people on the third floor felt it in their hips. By the sixth floor you only felt it in your glass of water. The rumble lost one body part per floor. By the roof it was gone. The pigeons on the roof had never felt a subway in their lives. They did not know they were standing on top of a river of steel.

The rumble changed the music. I played guitar on the corner above the Delancey Street station and every four minutes the ground shook under my feet and the guitar vibrated and a note I had not played entered the chord. The F train was a bass player who sat in without asking. The F train played in the key of B flat because that is the resonant frequency of the tunnel under Delancey Street. Every song I played on that corner had a B flat underneath it whether I wanted it or not. The subway did not care about my key signature. The subway had its own.

At three in the morning the rumble changed. The maintenance trains ran slower and heavier. The rumble was deeper. The building settled into it the way a body settles into a slower heartbeat during sleep. The building was sleeping and the maintenance train was its dream. The dream was about steel wheels on steel rails in a tunnel that had not seen daylight since the Roosevelt administration.

You did not miss the rumble until you left. You moved to Brooklyn or Queens or God forbid New Jersey and you slept in a building that did not shake. The bed was still. The coffee was still. The night was still. And you lay there in the stillness wondering what was wrong. Nothing was wrong. The heartbeat was gone. You had moved away from the body that had been breathing underneath you for years and now the silence where the rumble used to be was louder than the rumble ever was.