Clever Hans was the name of a horse in Germany in the early 1900s that was supposedly able “to add, subtract, multiply, divide, work with fractions, tell time, keep track of the calendar, differentiate musical tones, and read, spell, and understand German.”
Wilhem von Osten was Clever Hans’s owner and trainer, and proudly showed his horse’s remarkable talents to one and all without charging a fee. When asked a question, Clever Hans would tap a hoof or nod his head, responding not only to oral questions, but even those in written form.
Von Osten was obviously proud of his precocious steed, and willingly agreed to rigorous testing by an investigatory commission. Remarkably, Clever Hans was able to answer a large percentage of the questions correctly under test conditions, even when his owner was not present. This initial finding was startling and certainly ruled out the possibility that von Osten was perpetuating a fraud. But was Clever Hans really as talented as it would seem?
Psychologist Carl Stumpf, who ultimately took over the investigation on behalf of the commission, was able to debunk the notion that Clever Hans could do all of these exceptional tasks by demonstrating what has now become known as the “Clever Hans Effect.”
Stumpf’s breakthrough came when he turned his attention from the horse to those who were posing the questions. Again, even without his owner present, Clever Hans was uncannily accurate. But Stumpf’s realization was that the humans asking the questions were in fact sending subtle and unintentional visual cues to the horse. It was the posture of the humans, or other forms of body language that Clever Hans was picking up. Put simply, Clever Hans was, as magicians and gamblers might say, looking for “tells.”
The point I’m trying to make with this very brief summary of a story from long ago, is that the Clever Hans Effect is real, and magicians should give pause when considering what subtle clues, cues, or “tells” we send out when we perform. Many authors and performers have talked about the need to disguise our sleights, and to use misdirection or redirection to deceive our spectators. But the Clever Hans story reminds us that if an animal can perceive unintended information, certainly an observant human can.
Have you ever done a video of yourself doing an effect? Look at the effect on this website that I taped doing a bill switch. At the pivotal moment when the switch takes place you will see a very slight wincing in my face. It is pretty subtle and in my own defense I will tell you that when performing this trick for others (as opposed to watching myself on my computer) I am always talking and never looking at my hands. But my point is there is often an inner tension during critical moments of performance that may have outer manifestations.
It’s something to think about. Magicians will often mention a spectator “burning” their hands with laser-like concentration. I would argue that those in the audience who aren’t as intensely determined to figure out what we’re up to, may just as well perceive something is happening simply by some other inadvertent signal, thus undermining the success of our performances.