Comment by adrian_b

> An octopus cannot get through a gap that is too small.

True, but "too small" is considerably smaller than a human unfamiliar with octopuses would believe when seeing one, because, as mentioned in TFA, "too small" means "smaller than the distance between the eyes", which can be much smaller than the apparent diameter of the body.

Many years ago, the ability of octopuses to pass through very small gaps became widely known only after a large number of cases when octopuses had escaped from aquaria which were believed by their owners to be impossible to escape from.