In, out.
Splish, splash.
Clink, clank.
It is slightly maddening to hear these sounds over and over again. But to Sirius, they only mean one thing: tick, tock, tick, tock, tick, tock…
He taps a finger against the hard floor. Tick, tock, tick, tock.
There are times when he paces around his cell, thinking only of escape and revenge, when his bare feet sound a steady beat against the floor. He places a hand to his chest, and listens to his heart. His pace grows frenzied, his heart speeds up. Ticktockticktockticktock…He can feel it, his clock ticks faster, time itself speeds up.
And there are other times, when he lies curled up on his cot, tears streaming down his face, the silence accentuated only by a whimper here and a sob there, piercing the stale air. There is no tick tock now, he can hear nothing but the clanging of far-away chains, the lapping of far-away waves, and the ever present, not-so-far-away sound of his own ragged breathing. Time seems to slow down.
Either way, there's always a clock. Never stopping, ticking away, until…until what?
He doesn't know.