When I was an intern, we had a lecture about methods of smoking cessation. One of the interns was an ex-smoker and tried hypnotism to quit. She started talking about hypnotism and she said that it doesn't work for everybody. The way you determine who it won't work for is something called the "Eye Rolling Test".
I swear to god, I thought the test was going to be that if you rolled your eyes at the idea of hypnosis, you couldn't be hypnotized. Which let me out.
Apparently, the test is that you have the person look skyward and record how much of their iris and cornea are visible. The more of the whites of their eyes you can see, the easier they are to hypnotize. She tried it on me and said that I was a 3, which is the cut-off for someone who might be hypnotizable.