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From the depths of a federal jail on the Brooklyn waterfront, the sound reverberated: a polyrhythmic pounding like a hailstorm on the roof of a shed.

It was the sound of hundreds of men in freezing cells at the Metropolitan Detention Center in Sunset Park, a jail that was virtually without electricity and largely without heat for over a week. With the jail on partial lockdown, inmates were unable to use phones to call their loved ones, but their percussive banging could be clearly heard to those outside, and to the world beyond.

The inmates banged anything they could — shoes, their fists — against any surface they met: the walls and windows and bars of the jail that holds them.

Sunday morning, when protesters unfurled a long paper banner across the street from the jail that said “You are heard you are loved,” the inmates banged their approval.