Guardian Shark Shield Does not Affect Nurse Shark

I dangled the end of my Guardian Shark Shield Tail right on the nose of this nurse shark [Yes it was on I check frequently with my hand which gets shocked each time]. Hopefully this is unique to nurse sharks but thought have same biology as others? Internet says "They also possess electroreceptors called the ampullae of Lorenzini, which help them detect electrical fields produced by their prey.". I wish all the reef sharks I see would come in close enough to test. I need to shoot a small fish when reef shark around to test I guess. Have no data here as these are situations I tend to [successfully] avoid. In fairness have another video posted where it seems to work on a much bigger nurse shark so maybe size is factor.

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