busted

The sharks detected fish blood, however they either did not detect human blood or did not care about it. Also, like any scent, the sharks weren’t able to detect the blood until their noses came into contact with the blood particles, and the smell grew weaker as the blood got diluted by the water, meaning that a single drop of blood in a particular area of the pool would not be detectable by any shark that was not in that area, and was not swimming right into the blood.