He wanted some peace and quiet, but there was simply no way to find any.
The damned Death Eaters around him gradually quieted down, though. They were crazy, not stupid. If they made too much noise, they would attract the Dementors.
But—why did they get to be quiet?
He did not know how long he had lain there amid his chaotic thoughts when, at some point, Sirius suddenly sat up.
He sat in the darkness, looking beyond his cell, and said, "Bellatrix, Regulus is dead."
His voice was calm, as though he were saying, "The weather's not bad today."
Bellatrix's answer was equally calm. "Mm-hm. Wasn't he already dead?"
"Voldemort killed him."
"Oh, then he must have deserved it." Bellatrix giggled. "He must have defied the Dark Lord. Any filthy blood traitor who defies the Dark Lord—"
Bang!
A thunderous crash cut off Bellatrix's careless words.
Though their vision was swallowed by darkness, Bellatrix, along with the Death Eaters in the surrounding cells, could still vaguely make out Sirius's figure slamming violently into the iron bars of his cell.
Within that suffocating darkness, they could almost see his scarlet eyes.
Madness. Hysteria!
Sirius cursed in heartrending rage, "Bitch! You filthy whore! You heartless animal! That was your brother! Voldemort killed him—killed him—and you're saying he deserved to die!"
"Aaaah—"
His curses turned into a venting howl. That increasingly ragged voice was filled with inescapable regret and agony—agony so profound that it drove him out of his mind.
Again and again, he crashed into the iron bars with deafening force.
The bars shook, giving off an ear-piercing screech of metal scraping against metal.
Bellatrix had initially laughed as she watched his inexplicable fit, treating it as a joke, but her expression immediately changed. "You've gone mad! This will draw the Dementors—"