This is one of the less advanced senses of the shark. They primarily use this sense to determine if they will continue eating a meal, or reject it. Many people believe that when it comes to shark attacks, this sense is the reason that many sharks leave a human alone after the first bite.  They decide that we are not a high fat animal, so we probably are not that nutritious.  The same is true for otters: they belong to the same family as muskrats and they taste bad.