[Is it weird that one word makes him tense? Yeah. Probably weird. He can't particularly help it; for years now he's known something bigger and badder than Loki's girlscout troop is going to come along. Being stuck here when he could be preparing is driving him a little stir-crazy. And the way Sam says it?

Yeah, that's not in a good context. He shoves his paranoia down though, no need to jump all over the man with probably baseless worries.]

What aliens? We've met plenty of aliens. Thor's an alien.

[Okay, maybe he's met aliens and Sam's met...science experiments. Look, he can't help half the team when Sam was on it was bioengineered. Things happen. People get super powers. Just every day stuff.]