"Is the blood red?" is incorrect? I feel totally lost about when definite articles actually mean a definite article.
It should be accepted, too. But it definitely reads like a general statement.
------- how ironic it is that you've left out an indefinite article - where it's needed : ... a beta mistake... . but it's the same for both: if you're talking about a general class of things you don't need the article. once you're talking about a specific subset (of the general class "blood, mistakes " ), the blood on the knife, a mistake in the beta version, english-speakers would all use the article . . .
Big 13 nov 18