Now let's perform another thought experiment. I would like to ask you to imagine that the Harvard Group Scale is being given to a class of introductory psychology students at the American University of Beirut, let us say, when a person dressed in a police uniform bursts into the room and says in a loud, commanding voice, "The city is under biological attack, and a germ cloud is headed this way. Take refuge in the basement immediately and await further instructions!"
Even if such an announcement is a hoax (i.e., a cleverly-designed suggestion) thought up by a dissident student organization to disrupt the orderly running of campus activities, if it were to be conducted in a sufficiently convincing manner, everyone in the class -- including the instructor -- would probably dash for the exits and head for the nearest underground shelter.
Just as in our previous thought experiment, a high degree of responsiveness to the impostor's suggestions would occur regardless of how an individual student might have scored on the suggestibility test which was currently underway. Notice also that they would probably have been totally involved in the content of the impostor's suggestions: trembling, feeling frightened, weeping, crying out in alarm, and so on.
Suggestibility, then, only appears to be a trait of personality, because of the way our experiments are designed and carried out. But if a suggestion is believable enough, as in the hypothetical example just mentioned, individual differences in responsiveness instantly vanished as the entire class scrambled for the exits.
I used to believe that hypnotizing someone who scored low on the Harvard Group Scale was like trying to teach a snail to firewalk: it simply can't be done. Now, I am convinced that hypnotizing a person who scores low on a suggestibility test is more like teaching a person to dance who appears to have a poor sense of rhythm. We can't all be like Fred Astaire or Ginger Rogers, but almost anyone can learn to dance to a passable extent -- and with practice, some of us can become pretty good at it.
Lynn, S. J., & Kirsch, I. (2006). Essentials of clinical hypnosis: An evidence-based approach. Washington, DC: American Psychological Association.