Lie Detecting: A Bullshit Episode Penn & Teller Should Do

Penn & Teller haven’t yet done an episode on lie detecting for their Emmy-nominated series Penn & Teller: Bullshit! (which you can get on DVD). On Bullshit Penn & Teller expose, rip apart, and generally make fun of nonsense from talking to the dead to alien abduction to alternative, new-age medical mumbo jumbo to conspiracy theories to religion to college education to popular social misconceptions to big foot to politicians and government programs…

Well, here’s an idea they haven’t done yet, but which they ought to do, because it’s tailor-made for this show:

(UPDATE: They did an episode about polygraphs shortly after I wrote this post. Their research team, I’m sure, had already been hammering out the details when this post went live. Interestingly, they never got to most of the points I mention here. I guess lie detecting really is a huge load of bullshit.)

Lie Detectors

The polygraph, voice stress analysis, and now brain scans for lie detection. Unfortunately, these methods are only a step above ancient methods, such as a touching a hot iron to a suspect’s tongue, or having the suspect pull the tail of the Sacred Ass. (There’s gotta be a good Bullshit joke in there somewhere.)

Since you’re asking now, here’s how the Sacred Ass worked. What they told the suspects was that the ass was inside the dark, sacred hut, and it could tell whether or not you were guilty. If you pulled the ass’s tail and it brayed, you were guilty. But if it didn’t bray, you were innocent. What they didn’t tell the suspects was that they had coated the tail with lampblack. An innocent party, they supposed, would go into the hut and pull the ass’s tail. The ass then may or may not have brayed, but the innocent suspect’s hands would be covered with soot. The guilty suspect, however, afraid of being revealed, would not pull the tail in the dark of the hut, and when he came back out, his clean hands would betray him. Of course, what they failed to realize is that an innocent suspect might also refrain from pulling the tail, for fear that the ass would bray out and that he would be wrongly accused.

Similar methods are still used by modern cops, by the way, one of the subjects I address at Effective Interviewing and Interrogation Techniques (the link above) tells the story of a 1950’s police force who would have one cop ask questions while another stood behind the suspect with a large telephone book. They told the suspect that if he lied, he would get whacked in the head with the telephone book, and then they watched to see if he ducked. I guess they didn’t consider that even an innocent suspect, giving the “wrong” answer, might not want to get hit in the head with a thick phone book, even if he was telling the truth.

Under the same heading could also go the most hideous and deplorable of supposed truth-telling techniques: torture.

The research on lie detection isn’t much better. Some advocates of polygraphy and other techniques claim a 90% success rate… but not under real-world conditions, and not with suspects trained to use effective countermeasures. Even if that success rate were true, I’m sure it would be a great comfort to the 1 out of 10 people wrongly accused. There’s a reason why polygraph results are inadmissible as evidence in criminal trials: because the polygraph doesn’t actually work.

Frankly, Penn & Teller in their magic act do a better job of reading minds than most lie detectors.

Lie detection is bullshit!


P.S. If you’re from the Bullshit research team, here are a few resources to get you started:

A report by the National Academy of Sciences on ineffectiveness of the polygraph:

A New Yorker article on using brain scans to detect lies:

A video by George Maschke of, with a funny story of how some cops used a colander and photocopy machine as a lie-detector, and how this is no different than the modern polygraph:

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Late-breaking Government Opinion on Polygraph Privacy…

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