Optical illusions can play tricks on our minds and make us think we see things that aren't really there - but they can be fun to try and solve, especially when they involve hidden objects or are said to reveal personality traits.
And one recently shared illusion has been described as mind-boggling by some, as it appears to show an ape "evolve" into a man in the blink of an eye.
The bizarre video was caught on camera by a tourist who visited Hongshan Forest Zoo in Nanjing, east China on February 6, and happened to be filming a black crested gibbon through a window in its enclosure.
The tourist's clip follows the animal as it swings its arms and playfully hops onto a rock close to the window where she was filming, but as the camera pans across to continue following the primate, it appears to "transform" into a young man wearing a black jacket and a face mask.
As the man turns to look at the woman filming him, the footage ends.
'Covid ruined Christmas - if are not utterly selfish please wear a mask'The mind-boggling video has left viewers on social media stunned, the Daily Star reports, with many joking that the ape must have been a zookeeper in a costume, who managed to ditch his ape suit as the video transitioned.
One person said: "I knew it! Zoo animals are staff who dressed up in costumes."
While another added: "The zookeeper is off work, that's an impressive change."
And a third posted: "What an evolution – from gibbon to human in a face mask."
There were some commenters who were less than impressed with the video, as they assumed the seamless transition must have been the work of fancy camera trickery and editing skills.
But the woman, who wishes to remain anonymous, wrote on the video-sharing platform Douyin that the video was posted without edits and that the young man in the clip is actually her 17-year-old brother.
She captioned her clip: "Guys, this young man is my little brother and he is 17 years old. He is not a worker at the zoo and in the background, you can hear my little sister talking to me."