What's a shark's "yummy hum"?

If your ears picked up on a 40-hertz signal, you might wonder what the annoying sound was all about. But if you're a shark and you hear this "yummy hum," it might mean it's dinner time.

If humans have their dinner bells and Pavlov's dogs had their metronome, do other animals associate sounds with food? Possibly. There are some people who think that sharks in particular respond to something… » Full Story on HowStuffWorks