Their position was a compromised one, and though L's hold on Mello was firm, he couldn't exercise that same straight jacket-like effect on every part of his successor.

Without warning, the back of Mello's head (thick, hard bone) smashed into L's temple (thin bone, artery near the surface of the skin, weakest part of the skull). Taking a blow to the face would have been preferable. Had L known it was coming, had L not turned his face toward Bakura, the blow would probably have broken his nose. But he didn't even have time to register fully what had happened as sparks shot off behind his eyes, and just like that he'd slipped to the floor as Mello broke free, cheek against the dusty ground and eyes half-closed.

His arms were definitely not chains anymore. One was under him, the other limp at his side. That one, especially, felt alarmingly strengthless. And then there was nothing, just a period of thick darkness that L couldn't stave off.