Watching a hunt, if you are lucky enough to be still and the animal is busy with something that is not you, is a short story. The octopus leaves the cover, or strikes from it, and lands on the prey with the arms. Suckers do the holding. The arms pull the crab or the shrimp in toward the mouth, which sits where the arms meet, not out at the end of a limb. There is no chasing swim around a pool. There is a pounce and a gathering-in.
The beak does the part a soft body cannot. It is chitin, hard, and shaped for punching a hole in an exoskeleton or for biting into the joint where a shell is weaker. Through that hole, or from the salivary glands into the bite, the venom goes to work. Prey muscle fails. The struggle that would have torn an arm or cost the octopus a retreat simply stops. Then the meal can be taken apart without a fight.
People sometimes describe the human bite as tiny, even painless, and the hunting picture explains why that can be true. The beak is a tool for a small shell, not a weapon designed to announce itself with a wound you will notice. A crab does not need a dramatic injury. It needs to be still. The same standard applied to a hand is why a person can be envenomed and not immediately sure anything happened.
None of this is a technique to imitate or a scene to stage for a photograph. Baiting an animal into a hunt for the camera is how a warning display gets provoked on purpose. The pounce is interesting because it shows what the venom is for. It is not interesting as a trick to summon.