04Octopuses have blue blood.

Human blood is red because our blood contains haemoglobin, an iron-rich protein that transports oxygen. Octopuses blood contains heamocyanin, which contains copper (blue) instead of iron (red).

Copper is a better oxygen transporter in cold, deep waters where octopuses tend to live. It isn’t super efficient though, so octopuses have three hearts to compensate. They also take it easy on the cardio. Wise move, friend.

Source: How Stuff WorksExternal link