[His initial reaction to the laughter is to get defensive - but it's only when Kimblee speaks that Isaac realizes just how tense he is. It is just Kimblee, and even if Kimblee likes to tease him relentlessly, Kimblee's still the only person he can relax easily around.]

...Yeah, I know. I'm never really sure what to say.

[The smile returns then, a bit less excited than before, at least.]

Things are different now; I don't want to screw it up. That's all.