The Mona Lisa, painted by Leonardo da Vinci, is one of the most famous paintings of all time. Hanging from a wall inside the Louvre Museum in Paris, there is a mystery behind her piercing eyes.

Called the ‘Mona Lisa Effect,’ the story says that Mona Lisa’s eyes follow museum visitors wherever they go. It has been a fun fact for years, but experts have finally proven that it’s not true. Researchers from Bielefeld University’s Cluster of Excellence Cognitive Interaction Technology say that the effect is “undeniable and demonstrable.” They used 24 different test subjects, sat them at a computer with the Mona Lisa image on the screen and made them look at a ruler and tell which number at which her gaze was directed.

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Different parts of the paintings were used to make that conclusion. The ruler was placed at two different distances between the subjects and the monitor. The results were a little shocking, especially for those who believed heavily in the legend. Researchers found that her gaze wasn’t exactly straight-on but shockingly, Mona Lisa’s eyes landed on the viewers’ right-side and there is a little math involved.  “More specifically, the gaze angle was 15.4 degrees on average,” Dr. Gernot Horstmann said. He said that the effect is “nothing but a misnomer.” Hortsmann found that the effect only works “if the person portrayed looks straight ahead out of the image, that is, at a gaze angle of 0 degrees.”

With every legend comes some new way to prove it isn’t true. One doctor started that Mona Lisa’s smile is more of an indication that she had a disease. “The enigma of the ‘Mona Lisa’ can be resolved by a simple medical diagnosis of a hypothyroidism-related illness,” Dr. Mandeep Mehra said. The writer of a letter posted in Mayo Clinic Proceedings, Dr, Mehra, and co-writer Hilary Campbell, claims the subject had an underactive thyroid gland. It is easy to tell due to her skin tone, receding hairline, lack of eyebrows, and swelled hands.

Who knew you could diagnose someone through a painting?