Achilles ceased from speaking for a time, the words his mother was able to provoke causing him to be silent. In truth it had been some time, since seeing new faces that he had felt as himself. Bringing in old faces was a strong enough trigger to throw him to the ground. With all that energy put in their presence, it wiped him clean of energy to control his darkest of urges. Which had spun him out of control before. As much as that side of Achilles reveled in the sight of blood, gloated and became high off the rush---the other side was disgusted. It wasn't the way to live anymore.
Over time he had mellowed out, after war, when he had a chance to think outside of a battlefield. He liked the silence, it was comforting when he'd spent centuries with the terrified screams and battle cries. That silence had become to comfortable in a short span he found himself still pulled to the very battles that gripped him inside, which was where his hand in directing had came out. It gave him a chance to take back control, still be a part of all he'd known and have a connection with those around him. Suddenly, that wasn't enough though, nothing was enough when he continued to seek the absorption of glory like a wet sponge.
Then, people began to trickle into his life so suddenly, and that vivid part of his past was his future. His eyes shut at her touch, the stroke of his hair calming the irregular beat of his heart and the work up of emotions thrown in and out of his system.
In a moment of vulnerability, something he shared with very few, Achilles submitted to Thetis' wish. "Take it away," he whispered.