What is a fact that no one knows about?

One lesser-known fact is that octopuses have three hearts: two pump blood to the gills, where it is oxygenated, while the third pumps it to the rest of the body. Interestingly, when an octopus swims, the heart that delivers blood to the body stops beating, which is why they prefer crawling to swimming. This unique circulatory system helps them adapt to their underwater environment.