Constricting one's anus can work as a polygraph countermeasure provided that it is done timely with the asking of the "control" questions. This countermeasure so concerns polygraph operators that all federal polygraphers are required to use a seat pad that purports to detect such activity.
Alternative countermeasures include mental activity (such as thinking exciting thoughts, or doing math in one's head) and tongue-biting.
For more on polygraph countermeasures, see Chapter 4 of The Lie Behind the Lie Detector:
Re:Attempts to Censor AntiPolygraph.org
by DonHopkins on Saturday June 29, 2019 @08:34AM
(#20312219)
I'd love to be the government contractor providing all the expensive anal clenching divination seat pads.
Sounds like that would be a great input device for Affective Computing, Sentiment Analysis, and Targeted Ad Analytics. Maybe Facebook will make one to go with the Oculus some day.
If it actually works, the photo of Charles Wayne Humble in the article looks like he could lie through his teeth while passing a polygraph exam with flying colors!
https://en.wikipedia.org/wiki/Arpanet_(The_Americans)
After consulting with Arkady and Oleg, and with the promise of coaching from Oleg, Nina tells Stan that she will take the FBI's polygraph test. Oleg suggests a few techniques including that she visualize him in the room as well as clenching her anus.
https://www.youtube.com/watch?v=s3OMSMq9zPA
The Americans Season 2 Episode 7 "Arpanet" Review: "I like when I learn something from an episode, and now I know ..." "If you're having to do a polygraph, squeeze your anus."
https://tv.avclub.com/the-americans-arpanet-1798180091
(One of the ways to beat a polygraph turns out to be clenching one’s anus. This show is full of helpful hints.)
https://www.esquire.com/entertainment/tv/a28316/spy-on-the-a...
ESQ: The show featured Nina learning to beat and eventually beating a polygraph. How easy is it to do that?
PE: We have a number of real-world instances. The Aldrich Ames case. He went through the polygraph twice, after he went to work for the Soviets. Administering a polygraph is an art, not a science. That's why it's not admitted in court. People have claimed to have had training to beat the polygraph. Everything from tightening your sphincter to breathing a certain way, and so forth.
ESQ: Speaking of sphincters, the trick she's told is "squeeze your anus." Is that a thing?
PE: I can't confirm. [Laughs] I took several polygraphs. Taking them is a standard thing in the intelligence life.