An octopus can squeeze through any opening that fits its beak.

Octopuses belong to the class Cephalopoda, which are characterized by their lack of a rigid skeleton. Unlike their relatives the nautilus or the cuttlefish, most octopus species have lost all internal shells during their evolution. This anatomical freedom allows them to utilize hydrostatic skeletons, where muscle contractions against internal fluid provide movement and shape. The only rigid structure in an octopus is the beak, which is located at the center of its arms. This beak is composed of chitin, a tough nitrogenous polysaccharide also found in the exoskeletons of insects. Because the beak cannot be compressed, it serves as the ultimate physical limit for any passage the animal attempts to navigate. Research conducted at institutions like the Monterey Bay Aquarium has documented the incredible flexibility of the Giant Pacific Octopus. These creatures can compress their entire mass to fit through openings less than 2.5 centimeters wide. This ability is a vital survival mechanism for escaping predators like sharks and seals or for squeezing into tight rock crevices to hunt for crabs and mollusks. In one famous 2016 incident at the National Aquarium of New Zealand, an octopus named Inky successfully escaped his tank. He managed to squeeze through a small gap at the top of his enclosure and slide down a 50-meter drainpipe leading to the ocean. This event highlighted the species' problem-solving skills and their physical ability to navigate extremely narrow plumbing systems.