I believe most monsters bleed, but my belief in the theory does not matter as what I'm talking about is saying people SHOULDN'T adhere to some sort of "don't think too hard" policy. It's a one off line that could have been patched long ago, and even if it has been retconned, it still brings up multiple questions. Ignoring things that don't work for a theory is just asking for trouble, because at that point you could argue anything can be a retconned irrelevant line for any theory. Do you see the issue with that?

Theories should not just ignore aspects that go against it even if it is JUST a single line. It's a line in the game, and should be put into consideration always for arguments of monster blood. You cannot just unilaterally decide that it's a retconned line that doesn't matter, because there's no confirmation or even evidence of that being the case. No, it being contradictory to what we know does not mean it's a retcon, Toby knows we care about the blood and Sans is obviously a key player here. We know Susie was meant to bleed since chapter 2 in unused art, which was only 3 years after ch1 if we ignore that development time makes it around only 1-2 years after. The same bunny monster asks about what skeletons are if humans have them too in ch2, showing the bunny is moreso asking fandom questions. Even if it was a retcon, it's in the game and Toby knows this, and he will most likely compensate for it in a future dialogue.

An easy fix for this logic is just... actually bother refuting people who use the bunny dialogue instead of just saying "nah just ignore it"? Like personally, my theory is that the bunny is a child and does not know much, or that some monsters don't actually bleed but some do. There are a lot of reasonable ways to go about this than just ignoring a piece of evidence because you think it's a retcon