 And they believe those voices are outside, although we now know they are actually produced within their own brains. And the process there is actually quite sophisticated. Normally, when we are preparing to speak, part of our brain, which is making up the words, is switching off the part of the brain which is listening. Because if it doesn't switch off the part of the brain, it doesn't listen. We end up hearing our internal thoughts. And that's what happens with auditory hallucinations and schizophrenia.