Test: Dr Kallmes set up a revolutionary trial to test if fake operations could also heal damaged vertebra in the back. He found that patients who believed they'd been treated - but actually hadn't - recovered as well as those who really did have the op.
We've all heard of placebos. They're dummy pills. They can't do anything real. After all, there's nothing in them.At least, that's what we thought. But in recent years, evidence has built up to suggest that placebos can be highly effective - particularly in treating pain, depression, and even alleviating some of the symptoms of Parkinson's disease.
And it isn't just dummy pills that seem to be able to work: you could get life-changing improvements from a pretend potion that's actually just water; or perhaps fake acupuncture with needles that don't even puncture your skin.
The key is simply that you think it might help you. But when it comes to placebos, it doesn't get much more dramatic than what's been called sham surgery - as Dr David Kallmes discovered a few years ago.
He's a successful radiologist at the Mayo Clinic, one of the world's leading hospitals - it's where the Presidents of the United States often get treated. For the past 15 years, he's been fixing broken backs by injecting them with a special kind of medical cement.
Dr Kallmes regularly performed the procedure - called vertebroplasty - and found it hugely effective. 'We saw terrific results from the procedure, really amazing results,' he told me.
However, there were some questions as to exactly what was going on - because some people seemed to get better even when the operations went horribly wrong.