PTE AcademicReading
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How Octopuses Change Colour
biologyOctopuses can change colour in less than a second, a skill they use both to hide from predators and to (1) with one another. The change is controlled by thousands of chromatophores, small elastic sacs of pigment in the skin. Each sac is surrounded by muscles that are (2) linked to the nervous system, so the animal can expand or (3) it almost instantly. Surprisingly, octopuses appear to be colour-blind, which makes their skill at matching their (4) all the more puzzling. One (5) is that light-sensitive proteins in the skin itself may help them detect colour.