No, they can't hear the way we do, but they can feel some vibrations - for instance, Carol (corw314) used to tap three times on the tank to signal her bimac and she got a response.
So by all means continue talking to your octopus - it means you're there at the tank trying to interact and that has a long term positive effect.
Just curious if voice pitch made any difference, since I'm usually making silly high-pitched noises. I know they are sensitive to vibration, we have hardwood floors, and he gets very still when he feels us walking on the floor.
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