Their grip is no joke, as anyone who has encountered them while under water can attest.
From "Victor's Videos," the YouTube uploader:
while trying to get video of a wild octopus, it suddenly dashed towards me and rips my shiny new camera from out of my hands, then swims off, all while the camera is recording! he swam away very quickly like a naughty shoplifter. after a 5 minute chase, I placed my speargun underneath him and he quickly and curiously grabbed hold of the gun as well, giving me enough time to reach in and grab the camera from out of his mouth. I didn't feel threatened at all during the whole ordeal. he seemed to be fixated on the shiny metallic blue digital camera. the only confusing behavior was how he dashed off with it like a thief haha. cheeky octopus.
And remember, touching, poking, petting, or otherwise bugging marine life while in the sea is not cool.