I think the behaviour might have to do with the nose of the sharks, see how the diver keeps touching it? Sharks sense electromagnetic fields thanx to clusters of sensors on their head. Touching the nose might confuse those senses or influence them in such a way that the shark becomes docile.

The effect is called "tonic immobility" i know it happens with some sharks if you turn them upside down. Its said turning the shark upside down makes its electromagnetic sensors confused, so it might also work with touching the nose for some types of sharks.

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