The impression I got from Astonishing is that Sydren is supposed to be a psychic of some kind, but it doesn't function very well (at least the clairvoyance doesn't) so Brand gives him a hard time.
Sydren: "I sssensse desstruction."
Brand: "Really. You sure. You don't wanna to look at the photo of enormous destruction some more before making such a bold statement?...tell me you are picking up something besides "house go boom"".
Sydren: "If I ate your head, two thirdssss of your agents would praise me in poemsss and sssong."