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Did you know? Octopuses have three hearts—and two of them stop beating when they swim, which is why they prefer crawling instead. Their blood is also blue because it uses copper-based hemocyanin to carry oxygen, which works better than iron-based hemoglobin in cold, low-oxygen water. And if that’s not enough, each of its eight arms has a mini-brain, letting them taste, touch, and act independently even while the main brain is busy elsewhere.