Some fish, notably sharks, have a sense organ, the lateral line system, which picks up weak electrical signals in the water, alerting them to prey that would be otherwise invisible and possibly also helps with navigation. There's some evidence that this "organ" is ontogenetically related to the inner ear in humans.
Thought experiment: Say you're a shark, and a yummy snack is hiding just beneath that little pile of sand across the way. Your lateral line is going haywire, but you don't know from lateral lines because, hey, you're a shark, not an ichthyologist. So how do you feel? Off-balance? Out of whack? Or just hungry?
