The comic is getting at souls being kind of a silly concept that breaks down when you think about it. A lot of people mean "soul" when they say "consciousness", so although the comic says consciousness, I think it's poking fun at the idea of souls. I've never heard a good argument for them that doesn't boil down to "Wouldn't it be nice if it were true?"

I think that by soul, they’re really referring to the “self” - that sense of you being located behind your face, looking out into the world. I’d argue that’s an illusion.

Consciousness, on the other hand - at least to me - simply means the fact of subjective experience. The fact that it feels like something to be. And I’d argue that’s not at all unique to humans.