How Small a Space Can an Octopus Pass Through?

Remember the experiment mugumogu did to see how small a space Maru and Hana could get through? Octopuses are even more fluid than cats- the only rigid part of its body is the beak. How small a hole can an octopus squeeze through if he wanted to?

Arnold is an octopus who lives at Octolab. Arnold's favorite possession is his barrel, which gives him an incentive in this experiment. A transparent wall allows him to see the target, and a hole of decreasing size makes getting to it a challenge. Arnold eventually gives up, but we don't know if that was due to lack of ability or lack of motivation. After all, just because he can squeeze that soft brain through a small hole doesn't mean it's a healthy idea. (via Laughing Squid)