The shark is very likely only checking you out because it felt the vibrations in the water from a wounded fish and was coming to check for an easy meal. Being confronted by an noisy bubble blowing thing nearly 8' long with a long sharp appendage and foul temper is enough to convince the scavenger/predator that there is no easy meal to be had and they usually turn tail.
It is crucial to do this as early in the encounter as possible so that the shark does not get too comfortable with you and feels safe to approach and take a "nibble" of the fish.
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