A GIF created in 2008 has been making the rounds across the internet recently as viewers continue to be confused about why they can hear audio from the image file despite it containing no audio element.

The GIF in question—often referred to as “Pylon Skipping Rope” or some variation on that title—has become notorious for creating an auditory illusion that makes viewers think they can hear the silent image.

Created by a person using the handle IamHappyToast as part of a Photoshop contest on the online discussion board for b3ta.com, the GIF depicts a pylon “jumping rope” between two other pylons that are spinning a large wires that are connected across the large, metal structures.

When the jumping pylon hits the ground, the GIF appears to shake or vibrate, emphasizing the size of the structure and simulating what would happen when it hits the group. For some viewers, that vibration also generates a booming sound that people claim to be able to hear when the pylon hits the ground.

The image has gained traction recently after being shared on Twitter by Dr. Lisa DeBruine from the Institute of Neuroscience and Psychology at the University of Glasgow. She posted the image along with a poll asking her followers to report what they experience while watching the GIF.

The question received a massive amount of feedback, with more than 268,000 people participating in the vote. Nearly 70 percent of respondents reported being able to heard “a thudding sound” compared to just 19 percent who claimed to have no response to the GIF.

How people who perceived the “thud” varied. One person who suffers from hearing impairment reported hearing “a vibrating thudding sound” and claimed during the camera shake that it “cuts out my tinnitus.” Another said their seven-year-old child reported being able to feel the vibration but couldn’t hear it.

The creator of the GIF, IamHappyToast, chimed in on Twitter to report that the “thud” that most viewers were experiencing was “almost entirely in the shake” and would be heard even if the pylons were cropped out of the image. “They just give it height,” the creator explained.

Dr. DeBruine told the BBC that she received reports from some deaf and hard of hearing people perceiving the sound when watching the GIF. Even those with aphantasia—a condition in which people cannot visualize mental images—could “hear” the GIF.

A number of explanations about the perception of the audible effect poured in, but there did not appear to be a consensus that clearly explained the phenomenon. Chris Fassnidge, a doctoral candidate in psychology at London's City University, suggested a theory called the “visual ear.”

According to Fassnidge, the “noisy GIF” is related to the Visually-Evoked Auditory Response (vEAR) effect. He described it as “the ability of some people to hear moving objects even though they don't make a sound, which may be a subtle form of synaesthesia—the triggering of one sense by another.”

He explained that because we are constantly surrounded by movements that make a sound, we are able to perceive that sound when we see the action it is associated with—even if no sound is being made. It is possible to hear footsteps when watching someone walk across the street even if those footsteps are not actually audible, for example.

More GIFs like “Pylon Skipping Rope” can be found on the Reddit community r/noisygifs, which has collected a number of images that produce the same phenomenon.