ink sac

Ventral view of the viscera of Chtenopteryx sicula

An ink sac is an anatomical feature, an ink-containing organ of a cephalopod (octopuses, squids and cuttlefish). This sac can release an inky fluid from a duct opening at the base of the siphon in order to confuse its enemy or prey, or as cover to escape. A general level of provocation is necessary to trigger an octopus to release its ink, as it is biologically costly to produce. Some species can even use their ink to stun or numb their predators.^{[citation needed]}

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