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I read about a phenomena called 'otoacoustic emission' in an article at newscientist.com where there was a dog who seemed to be humming everywhere he went. Here's an excerpt from the article: "In this condition, the normal hearing pathways in the ears are somehow reversed, so that the cochlear efferent nerve fibers stimulate outer hair cells to vibrate and make a noise. Other parts of the ear such as the tympanic membrane can then amplify the sound, until you end up like Zoe, humming wherever you go."
Zoe, as you might have guessed, was the dog.
Never letting a weird thought go to waste, here's a suggestion on how we could turn that condition into something useful. People who have had a severe spinal injury can enter what is called a 'locked-in state', meaning they are so paralyzed that there's no way for them to communicate with the outside world. If a cochlear implant was designed so that it could create these otoacoustic emissions on demand then it might give these patients a way to communicate. With a little biofeedback training they could vary the sound waves that are being emitted and establish a new form of communication.