What number do you see in this picture? The viral optical illusion takes the internet by storm.

Editor's Note: This article was originally published on April 1, 2022. It has since been updated.

People have found a new optical illusion to obsess over. A seemingly simple image shared by Twitter user @benonwine features a number partly concealed within a striped black and grey circle. "DO you see a number? If so, what number?" they ask in the tweet. While this initially looks like a fairly easy task, you soon realize that the zig-zag pattern of the circle makes things a bit tricky. Thousands of internet users from around the world have viewed the visual puzzle since it was posted on Twitter and have been baffled by how many come to very different conclusions about the hidden figures. 

Chances are, the number 2 jumped out to you almost immediately. Maybe you were also able to make out a "528" or "4528" without straining your eyes much. Many said the number is "45283" while some others claimed they saw the number as "15283." The correct answer, as it turns out, is seven digits long. Closer inspection reveals that the number is "3452839," a fact that baffled many Twitter users who weren't able to make out more than 3 digits within the swirly circle.

"45 283... and what's the catch? Should I book an appointment with my GP?" asked @PhilippeAuclair. "3452839. Can some people actually not see the end numbers even when it’s pointed out to them?" tweeted @NickEd82. "3452839. Strangely, this is also the telephone number of an Islington flat where Arthur Dent went to a fancy dress party and met a very nice young woman whom he totally blew it with..." commented @citysleuth. "Funnily enough, when I click on reply and it gives me a thumbnail, it's much clearer. Because it’s not moving, I guess? Anyway, 3452839 BUT 528 was clear, 45283 was more visible in some lighting than others, and the 3 & 9 at the ends were hard to see at all," tweeted @chronicleflask.

"I'm guessing the numbers you see depends on your 'contrast sensitivity' (different from what a standard eye measures). It can be tested by opticians. Worth doing if you're struggling, as it can affect your ability to see at night, or in [the] rain, fog, etc," @LittleToRelate helpfully explained. According to Vision Center, contrast sensitivity is "the ability to distinguish between an object and the background behind it."

"Contrast sensitivity is different from visual acuity, which measures how clear your vision is at a given distance.  High spatial frequencies make up detailed features such as sharp edges, facial features, and similar. Low spatial frequencies are more like coarse images, where you can see the overall shape of something but not detailed features. A contrast sensitivity test measures how well you can tell the difference between light and dark," the website continues. "For this, your doctor will use a different type of chart where the characters fade from black to gray gradually. Visual acuity is measured when you read the eye chart during an exam. This is considered a high-contrast test (black letters on a white background). You can have excellent visual acuity, but reduced contrast sensitivity and vice versa."

It is necessary to have good contrast sensitivity for safety when driving in low-vision conditions such as rain, fog, low light, or glare from a light source. "Numerous studies have shown that contrast sensitivity is a better predictor of driver visual performance than visual acuity. Contrast sensitivity helps you see road signs, pedestrians, curves in the road, and the difference between the street and sidewalks," the website states. "Having a contrast sensitivity deficit significantly increases your chance of getting in an accident." So what did this optical illusion tell you about your contrast sensitivity?