This is a video from the octopus research and knowledge group Octolab of Arnold the octopus attempting to squeeze through narrower and narrower gaps to reach his favorite hiding spot, a barrel. Some more info while I squeeze my arm up through the vending machine chute for a free package of powdered donuts:
We’re constantly being told that an octopus can fit through any hole. As long as he can fit his beak through a small space, his entire body will follow. We decided to test this out ourselves. …In no way was the octopus in this video placed in harm’s way at any time. The octopus in this video weighs about 4 pounds (1.8 KG). He measures approximately 30 inches (76cm) from the tip of one arm to the tip of the opposite arm when he’s stretched out. The spaces he attempts to go through in this challenge are
0.70 inches (1.7cm)
0.79 inches (2cm)
0.98 inches (2.5cm)
1.18 inches (3cm)
1.38 inches (3.5cm)
After making an amazing number of successful attempts, Arnold decided that was absolutely done.
TL;DNR easily into your butt, no problem.
Keep going for the video.
Source: Geekologie – Experimenting To See How Small An Opening An Octopus Can Fit Through