His brief amusement doesn't last as Daniel continues to go on. Especially when he reaches the killing bit, and just the look on his face.

"You might want to just avoid him from now on," Seth suggests mildly. That is definitely Seth's strategy. He knows he wouldn't stand a chance, and he figures he's probably enough of a coward to follow through on this strategy. (Never mind the time he stopped a zombie apocalypse, or the time an alternate version of him apparently defeated the Nazis.)