A few optical illusions have made their way throughout social media in recent months. Some can be explained through various psychological theories. Others have sparked much discussion, such as the infamous black and blue dress. Others are merely a way to kill time while reading an article online.
Which category do the following fall in? You be the judge.
A hidden object can be found in the latest optical illusion to make its way around the Internet.
At first, the photo appears to be a brick wall with a rock lodged in between two of the bricks -- an ordinary brick wall. But once you see the optical illusion it will be difficult to see anything else.
The rock is actually a cigar.
In April 2016, one of the most common optical illusions sparked discussion as BBC Academy trainer Marc Blank-Settle posted a video of part of his child’s toy on Twitter.
"My toddler's train track is freaking me out right now," he wrote. "What is going on here?!"
In the video, two pieces of a train set are positioned side by side. At first glance, the part on the bottom appears to be longer.
But when Blank-Settle placed it on top of the other piece, they appear to be the same size.
“That is going to give me nightmares,” someone replied to Blank-Settle, reported the Daily Mail. “I do not like it.”
This trick can be explained through the Jastrow Illusion, which was described in 1891 by Joseph Jastrow. The shorter side of the bottom track is being compared with the longer side of the top track.
"You have rediscovered the Jastrow Illusion, in a cool way," tweeted Tom Stafford.
Professor Michael Bach explained the illusion through an edited Jastrow quote, which demonstrates the way one can "judge relatively even when we most desire to judge absolutely."
"In judging areas we cannot avoid taking into account the lengths of the lines by which the areas are limited, and a contrast in the lengths of these is carried over to the comparison of the areas," the website reads.
The duck-rabbit illusion is another demonstration of this illusion, of which research has suggested that people who are more creative can switch between both images more easily than others.