How Octopuses Squirt Ink

Octopuses have one big heart that pumps the blood around their bodies and down into all their eight legs just like our heart does. Then they have two smaller hearts to pump blood to their gills. So why do they need three? They don't carry oxygen around their bodies the same way we do. We have red blood because that's full of iron. Iron is really good at carrying oxygen. But octopuses blood is blue as it's full of copper. Copper isn't as good at moving oxygen around the body so they need a bit of extra help and a couple of extra hearts. Ewan, five years old: How do octopuses squirt ink out of their