The old man took a step back from this battle he was fighting with Cerberus. It didn't seem like just slashing at it the whole time would end up working out well for him considering that Cerberus would always just keep on growing and growing in size.
Eisen tried to shrink down again and hack at Cerberus to see if it was going to shrink down again, as if trying to match the old man's size, but that seemingly wasn't the case. And then, Eisen understood the 'metaphor'.
Cerberus was basically an incarnation of Gluttony, or rather, the concept of 'Hunger'. The more you tried to get rid of it or supress it, the stronger it would grow. But what could he do to beat this monster then? What could Eisen do to beat it? He couldn't just 'accept' it somehow, since that would mean he had to be eaten up by it, and that didn't seem like a pleasant experience.
