Is octopus ink poisonous?

When alarmed, the octopus squirts out that cloud of inky liquid behind it. The cloud is like a smoke screen to cover its escape. The brown or black cloud is inky because it contains a lot of a common animal pigment, melanin. In fact, the original sepia ink comes from the ink sacs of cuttlefish, which are close relatives of the octopus.

The ink may also contain some chemicals that poison the smell receptors and help discourage a predator. But I think the smoke-screen effect is more important.