I've seen a lot of chatter about that specific moment, and the reason Sukuna shouts isn't just random rage. It's a culmination of frustration mixed with a kind of twisted respect. He's the undisputed 'King of Curses,' a being who views everyone else as beneath him, yet here's this shikigami, summoned by a human no less, that is actively analyzing and adapting to his cursed technique in real time. Sukuna's whole fighting philosophy is about overwhelming power and dominance, but Mahoraga represents a puzzle he can't instantly crush. The shout is his raw, visceral reaction to a challenge he didn't anticipate—a crack in his absolute authority, however temporary. It's the sound of his ego being grazed, and for someone like him, that's an intolerable sensation.
That scene gains another layer when you consider it from Sukuna's perspective as a connoisseur of strength and technique. He's bored by weak opponents and fascinated by interesting ones. Mahoraga's 'Adaptation' ability is, in its own way, a brilliant and unique power. Sukuna's scream isn't purely anger; it's also a kind of exhilarated acknowledgement that he's finally found something worth properly dismantling. He's been in a holding pattern, playing with his food up to that point, but Mahoraga forces him to get serious, to think strategically about how to destroy it before it fully adapts. That outburst is him shifting gears from casual cruelty to focused, brutal execution, and the vocalization is part of that intense focus and release.
The animation and voice acting sell it perfectly, turning it from a simple battle cry into a character-defining beat. You can hear the sheer, unadulterated intensity in his voice—a blend of fury, excitement, and a warning. It signals to everyone watching, both the characters in the show and the audience, that the gloves are officially off. After that scream, the fight escalates completely, ending with Sukuna needing to use his trump card, the Malevolent Shrine. It's the pivotal moment where his façade of effortless superiority slips, just for a second, revealing the volatile and terrifying warrior beneath. The moment sticks with you because it’s so raw and perfectly captures the shock of seeing an untouchable force finally, genuinely provoked.