Seth realises his mistake just before Daniel asks. Crap. Well, Daniel probably has a right to know, or at least it might make it easier to see where the other one is coming from. But he probably would've eased into, approached it from a different angle.

And then Daniel points his gun at Seth, who jerks back as if struck, raising his hands defensively.

This definitely was not the way he wanted to test the phasing through bullets theory. The viciousness and sudden hostility aimed at him does a good job of knocking down most of the emotional stability he's built up as they've made their way through the city, all in one single moment.

"No," he answers, not even sure what he's objecting to, he just knows that whatever conclusion Daniel's drawn, it's wrong. He swallows, suddenly terrified, his entire body stiff. "Whatever that-- I don't--"

Words seem to fail him at this point.