Can These Actually Read Your Mind?

Can These Actually Read Your Mind?

When you place the tentacle in your hand, something strange happens: it might curl up, or flip end over end, or the edges may twist in towards each other. What’s happening? The tentacle reacts that way because it’s made of a special polymer that absorbs water, and it’s reacting to the moisture on your skin.


That polymer is sodium polyacrylate, a hygroscopic material that really likes to absorb water. How much? It can absorb up to 800 times its weight in water, assuming that water is pure; for H2O with other dissolved minerals (like tap water), it absorbs around 300 times its weight. Sodium polyacrylate is more common than you might think: it’s the same substance used in disposable diapers, an application where you really want to make sure you’re absorbing as much moisture as possible. It's also used in wound dressings, and for entertainment as artificial snow – and fortune-telling tentacles, of course.


The water absorption is happening through osmosis: sodium polyacrylate, as you can probably guess from the name, has a lot of sodium atoms it. Water molecules are drawn to the sodium ions, and end up being absorbed by the polymer. But here’s the thing: it only absorbs those molecules when it’s in directly contact with the water. As you hold the tentacle, the molecules on the palm side absorb moisture from your skin and start to expand, but those on the side facing the air don’t; that causes the tentacle to change shape. 


What’s amazing is that this trick seems to have been used for centuries, long before the discovery of chemical compounds like sodium polyacrylate. In fact, the first known appearance of this kind of magic trick is in 1786, where it’s mentioned in the Testament de Jérome Sharp, a book by early modern magician and teacher Henri Descremps, in which he exposed other magicians who claimed to have paranormal powers. Your box contains books by one of his modern descendants, Martin Gardner, who both loved magic tricks and was famous for debunking claims of pseudoscience in the 20th century.


Descramps wrote about a trick where a magician would take a small piece of paper with a picture of a baby, and give it to two women. When it wiggled in the hands of one of them, that “proved” that she had given birth before (you’d think this would be easy to prove or disprove, but apparently people bought the trick). So what did they use three centuries before the discovery of modern hydrophilic polymers? It’s unclear, but it appear the “paper” in this case was probably onionskin.


It may have started with babies in the 18th century, but your Mind Reading Miracle Tentacle is one of a long line of fortune telling shapes used in the trick; over the years there have been fortune-telling mermaids, soldiers, leaves, Santa Clauses, and Yogi Bears. The best known is probably the Fortune Telling Fish, which seems to date to the 1920s. Hundreds of thousands – possibly even millions – of these fish have been made; a restaurant in New York City used to give one out with every order, and a mind-reading fish was included with physical copies of Leonard Cohen’s 2010 album “Songs For the Road.”


So does it work?  Well, the tentacle material reacts to water, and the moisture of your skin does change. The way scientists measure it is through your skin conductance response (SCR); basically a test of how well your skin conducts electricity, which primarily happens because of more or less moisture. Studies show that your SCR changes with both positive and negative emotional stimuli, as well as visual cues that evoke those stimuli. So in a way, an object that reacts to that moisture can in fact say something about what going on in your head.


We won’t make any claims that the tentacle is actually reading anybody’s mind, or truly displaying your emotional state, but it’s interesting to see how the idea of reading minds through skin moisture has some basis in real neuroscience. Truly mind reading or not, we hope it helps amaze your friends! 

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