When octopus and squid move through the water, they are using a form of jet propulsion to do so. The octopus and the squid can both squirt a cloud of dark ink into the water to try and confuse predators. There is a school of thought that the giant squid may in fact, fight back ferociously when attacked by predators. Sperm whales have been found with deep gashes around the mouth area, which might indicate the shark beak of a giant squid, fighting for its life. It is thought that squid communicate with each other through their ability to change colour.