Here's a report about research into the mechanism of the hammerhead shark's incredible sense of smell.
It is said that hammerheads can smell a drop of blood up to one kilometer away. How the hell is that possible? I'm not surprised if the sharks can detect really, really small amounts of certain molecules. Rather, I am surprised that any blood molecules appear up to a kilometer away. Obviously, I understand that can happen, but the way it is told, it sounds like you drop the blood in the water, and next thing you know the sharks can smell it, and that seems impossible. Can two hammerheads located two kilometers apart both smell blood right in between them? Does the blood really diffuse that far, and that fast? How fast? Is this diffusion isotropic?
All that is Silver is not Fish
3 hours ago in Catalogue of Organisms