the contemporary folk model of biology ("Blood is what keeps you alive, we're not quite sure how though, but in general try not to lose your blood"),

This sounds sensible, though it should be mentioned that bloodletting (hm, there's clearly too much blood here) seems like a candidate for folk biology as well.

(I once had a small, dark bruise underneath a partially healed cut- so it looked like there was this black thing inside my finger, though I was reasonably confident it was just a pool of blood. The urge to cut it open and drain it was unbelievably strong, and I had to put a bandaid on it just so that I couldn't look at it. After that I had a lot more sympathy for people who thought bloodletting was a sensible treatment. I suspect that particular incident was an anti-parasite impulse which mistakenly pattern-matched the pool, and I imagine most bloodletting was inspired by "you're way redder than is healthy- let's fix that!".)