Despite the fact that Irahl has become slightly more vocal in his time knowing Vincent, he just as often banks on Vincent knowing him well enough to not expect an audible acknowledgement of everything he says. So, when Irahl does make a sound, it's still significant in some way.

This time, the acknowledging grunt that he gives sounds like a knowing one. While he might not identify with Vincent's desire to live down in the dark, these thoughts somehow resonate.

It's probably attached to something significant, but of course that's not what he says when he does finally use his words.

"Won't bump your head as much, though."