It's when the earth around them collapses that Estinien realizes his desperate desire to put Gen down has played against his better judgment. If he had focused all his attention on escaping the pit, he could have easily avoided this outcome - but instead his attention had been drawn to that miserable little bastard and how much he wanted to tear him limb from limb, to make him feel the helpless despair Estinien had in their last encounter.

It was a mistake, surely, to let Estinien get so close. Yet, the greater mistake was Estinien allowing himself the indulgence.

He leaps at the precise moment he realizes what is happening, but the earth falls quickly enough that his lower extremities don't make it clear in time. His tail and wings, so constricted by the tight space, are buried along with his lower half. He is strong, especially transformed as he is, but the earth is heavy - it's only when he's straining against it that the impacts Gen made against his chest and leg really start to process.

In the meantime, Silco is free to make his appearance... and Estinien realizes fully that things are about to take a turn for the worst.