His silence just shows that he is probably observing or analyzing his current situation. Trowa has a very gentle soul that is hard to see at first.

One very important person of Trowa is Catherine Bloom. Though unknown to each other, they are siblings but this doesn't matter since they already act like ones. As he befriends her and gets to know her, Trowa's motivations for life become more apparent. She was someone that Trowa could return to when everything was over. He wanted to protected her and the circus, his family.

Since Catherine IS his sister, Trowa Barton is not Trowa's real name. He was separated from her when he was very young (his parents died), Trowa was just a nameless person. Eventually, when the Heavyarms was being built, he witnessed the death of the REAL Trowa Barton. It is here that Trowa decided to take the place of the original pilot and his name. And the rest, is history...