By: Lifestyle DeskNew Delhi | December 15, 2025 08:30 PM IST 4 min readDakota admitted that the first time she gave a lie detecting test for Vanity Fair, she 'fully lied' (photos: wikimedia commons, freepik)Lie detectors are often thought to be the ultimate way of finding out whether someone is telling the truth, right? Well, that might not always be the case. Dakota Johnson recently dropped a bombshell on the Good Hang With Amy Poehler podcast, admitting she once lied on a lie detector test, yet “passed”. When Poehler suggested that the lie detector test might be rigged, the actor countered by saying “I’ve seen other people, and they’re like ‘that’s a lie – that’s a lie’ and you see the thing.” On being asked if she thinks having a low blood pressure might be the reason behind it, Johnson fully agreed while jokingly suggesting that she could be a good spy.But is it true that having low blood pressure can give you a free pas on a lie-detecting machine? “A lie detector, commonly referred to as a polygraph, relies on more than one reading,” explains Dr Dimpu Edwin, Consultant – Interventional Cardiologist at Aster RV Hospital, asserting that Johnson’s assumption might not be accurate. Lie detectors mainly measure changes in heart rate, blood pressure, breathing, and sweating (photo: freepik)Can low blood pressure really give a false negative on a lie detector? Dr Edwin says, “It measures heart rate, blood pressure, breathing rate, and skin perspiration. So, even if your blood pressure is naturally low, you won’t automatically fool the machine—low BP is only one of the many factors.”He goes on to explain how the polygraph actually works. “The polygraph looks at variations during the question-and-answer phase. People with low BP do have a slower heart and less pressure, but the instant they get stressed, anxious, or guilty, their body reacts. A slight increase in heart rate, changed breathing, or sweaty palms can be detected. The machine doesn’t care about your BP being low; it’s the pattern it notices.”Before the test begins, operators take a baseline. “They ask easy questions like your name or age,” Dr Edwin says. “If your baseline shows low BP, all subsequent reactions are measured against your normal readings, not someone else’s. That’s why low blood pressure isn’t an advantage.”Of course, polygraphs aren’t perfect. “They can misread signals,” Dr Edwin warns. “Your body might react to nervousness, fear of rejection, or even overthinking, rather than lying. That’s why polygraph results aren’t considered strong legal proof in many places.” View this post on Instagram A post shared by Good Hang With Amy Poehler (@goodhangwithamy)The real reason behind these false results“When a person lies, the body usually produces stress, causing these signals (changes in heart rate, blood pressure, breathing, and sweating) to rise, but someone with low blood pressure may not show strong or sudden changes, making the machine think they are calm,” Dr Sanjay Bhat Sr. Consultant – Interventional Cardiology- Aster CMI Hospital, Bangalore, also weighs in. The cardiologist asserts that while the “person’s heart rate might stay slow, their breathing may not change much, and their sweat response may be mild, so the polygraph needle does not move sharply.”Moreover, some people with low blood pressure often feel relaxed or tired: “This constant calmness can hide stress signals during the test”. Dr Bhat clarifies that since lie detectors are not perfect and can be confused by medical conditions, anxiety levels, or natural body differences, a person with low blood pressure might appear honest even when they are not.Story continues below this adSo, what does this mean for Dakota? Basically, she wasn’t cheating the machine with her low BP—she might have just gotten lucky, or the machine misread her stress levels. “The machine is not controlled by actual BP. It’s the stress-related changes that the polygraph observes,” Dr Edwin concludes. For more lifestyle news, click here to join our WhatsApp Channel and also follow us on Instagram© IE Online Media Services Pvt Ltd