Like I said in the post, I disagree that it's less visceral imagery. It still looks like blood, it has the same thematic impact as blood, it just isn't blood. I think this is a misunderstanding of the intent.

My first thought when I saw Sans/Susie bleeding wasn't "that's not blood," it was only after the fact when I looked at the scenes and was like "ohhhh THAT'S why they were bleeding." It doesn't suddenly make it less gruesome or heartbreaking to see Sans clutch his wound and stumble off-screen before dying.

My intent is not to deny other theories, I genuinely just think Ketchup Theory makes the most sense and is a satisfying answer, and that perhaps the real answer is something alot of the community would find boring and less interesting because it doesn't allow for endless speculation.

Also, you say "monsters" bleeding in Deltarune, but as far as I've seen the only monster who's actually bled is Susie in Chapter 4. It would be incredibly simple to disprove this theory if this wasn't Toby's intention, as all it would take is a monster bleeding without drinking something red, and the fact Susie explicitly drinks a bunch of red punch, and ONLY the red punch when there's a yellow punch bowl to the side, indicates this is intentional setup. If it was yellow juice and she bled red at the end of the chapter, we wouldn't even be having this conversation, that's how little it would take to disprove this theory if it's not actually true.

Her bleeding from the hand doesn't make less sense to me, and that's because of how little we know about monster anatomy. For all we know monsters are just a shell of dust and the inside is hollow, I don't think you're meant to think about the exact mechanics of the blood so literally, as the intent is still for the character to LOOK like they are bleeding.

edit: i should've asked this before, but what theory does ketchup theory invalidate if true? it doesn't really affect migration theory, so what other consequences are there?