(When you are fighting sans on the surface he gets tired and you slash at him one last time and leave a big slash wound across his chest and then he says this.)

Heh, you got me again... yknow you caused so much pain for us that nobody deserved it, but I can't just die right here, not yet. I will strike you down one way or another.

(As he says this his right eye starts flashing blue and yellow, a yellow and blue gaster blaster also appears at his sides and he starts to attack you.)