Want to put someone through "humanity test," like the Bene Gesserit did in the Dune series? First you'll need a needle filled with "meta cyanide." That, I can't help you with. Then you need a box that can cause burning pain without harm. It's all possible if you use the "Thermal Grill Illusion."


The Thermal Grill Illusion gives people a feeling of burning pain, even when nothing damaging is happening to their body. The key is putting pleasant warmth and pleasant cool together, which unmasks a pain receptor that kicks into gear without any harm being done.

The Thermal Grill Illusion was first described back in the 1800s, just as soon as heating and cooling things became relatively easy. Just set out a "grill," with metal bars right next to each other. Cool down half the bars. They don't have to be really cold, just noticeably cool. Then heat up the other half of the bars, again, only to a pleasant warmth. The trick is interspersing the two, so anyone putting their hand on the grill should feel warmth, then coolness, then warmth, then coolness.


They should feel that, but they won't feel that. What they'll feel is burning painful heat instead of coolness. You feel something similar if you let your feet get really good and cold, then pour warm water over them. Without any damage being done to their hands, the person will feel pain.

The contraption isn't that hard to rig up. One scientist did it by interspersing microwaved hot dogs and frozen hot dogs on his kitchen counter. Any chilled and heated cylindrical objects will bring on the illusion. You could do it with anything from otter pops to actual metal bars, if you want to try out a thermal grill but don't have the skill to rig an electric heating and cooling grill. Enclose the device in a box and you have your pain-inducer.

How does the illusion work? Scientists have studied it many ways, from the nerves in the hand to the reactions of the brain. They think that a certain receptor in the nervous system responds to extremely high temperatures, extreme low temperatures, and the sensation of pinching pain. That receptor is masked when other receptors pick up a cooling sensation. The close proximity of the cold and the warm reduce the input of these masking receptors, and so the receptor that tells us we are being subjected to some kind of painful temperature is the loudest voice in the room, so to speak.


If you meet a Bene Gesserit sister, and they force you into a thermal grill test, be comforted that your hand isn't actually being fried. Invoke your Litany Against Fear and power through it. You're fine. But just to be sure, sniff. If you smell burning meat, they're just grilling your hand.

[Via The Thermal Grill Illusion of Pain, How the Thermal Grill Illusion Tricks the Mind.]