"if" in a story: "'if alive, may the sea foam milk. If dead, may it foam blood.' it foamed blood…"

What is the point of including ifs in a story? It will only ever have turned out one way, and the reader or listener will know that it only turns out one way (or in the above case, is only a confirmation of what has already been told), so it's stlye, or cruft – mere setup for an anaphora immediately resolved.

So we then ask the aesthetic question: why this? Why must it be the seafoam that is called upon, why milk, why blood?

The grandeur of the request is part of the point; the magic indicates Fate, the will of the Narrative brought to foreground. We have the alliances and associations – the sea's ties to the snake-king, and the sea's right to mourn, to rage; cast in the asking as an actor, an ally, where we would see set dressing. A world that is alive, but only revealed responsive in the moment of crisis; perhaps with the implication that anything at all might answer if it mattered enough. The if tees up an anthropic perspective.

The revelation is metonymic: the daughter and bride has been betrayed, and the moment of revelation an internal event rendered external not just in its consequences, in the sequence of the plot, but in its precipitation writ large upon the world. The internal drama continues to be writ onto the external: "…she turned herself and her children to trees in her grief…"

The anaphora lets us experience-alongside this revelation, gives the story a way to show-not-tell a critical plot beat that can't otherwise be shown; the poetic power of this active setting, the magic of it, is then made available to weight the if. – when built like this, she has to ask the question out loud, and we can listen with her; we have to parse the mechanics of what is supposed to happen, we have to perform the small task of matching the milk and the blood to the yes and the no, and in the brief pooling of our attention here we feel the milk and the blood. It recreates the pause…we can experience her dread, her doubt.

Related, as everything is, to poetics of structuralism.