[Okay, so. Everything about what she just said is amusing. There absolutely is such a thing as souls in his world, he should know, and the fact that a goddess is looking so visibly upset... Heh.
Sebastian's amusement doesn't show in his expression, however - his small smile is gentle, sympathetic.]
So some believe is the case. They are few in number, however... and perhaps something is to be said for the beliefs of many. [Speaking of more hilarity. Humans believe the stupidest things en masse.]