A smokescreen through ink clouds is one of the octopus’ main survival strategies. The behavior is prevalent in almost all cephalopods except Nautilus and some of the deep-sea octopus. The ink bag, a bulb-shaped bulge provided from the gut, is in squids placed on top of the liver, and in the octopus sunken in the liver. In most species the ink contains melanin, a black dye. Some deep-sea squids, Histioteuthis and Sepiella, have strongly luminescent ink immediately after it is sprayed. The ink of Octopus bimaculatus contains substances that apparently can paralyze a moray eel’s sense of smell, which then cannot find the octopus in an aquarium. It is uncertain whether the ink has the same effect in the open sea. For the octopus its own ink can be toxic. Observations of squid in aquariums with high concentrations of the individual’s own ink has resulted in death. Squids can spray the ink out in a cloud of almost the same shape as itself. The cloud can keep its shape in several minutes and look as if the octopus is still there, but in the meantime it has disappeared. Several observations of a pursuer attacking such an ink cloud has been recorded.