Sharks can sense the electrical fields generated by the nervous systems of fish. That looks like a vacuum cleaner attachment on the front of a hammerhead shark kind of is a vacuum cleaner attachment, or maybe a mine detector - use whatever human analogy you will. But the platypus is the only mammal that can sense electrical fields. Or so we thought, until one species of dolphin proved to have it, too.
COMMENT: Dolphins have big brains, smart hunting strategies, sonar, AND electrical sensing? Fish are screwed.