Everyone knows the famous 1930 optical illusion where it could either be a drawing of an old woman or a young girl.
Now, almost a hundred years later, a Twitter user posted a similar illusion, but with a bit of a twist. Do you see a playful pet or an evil horse-pig hybrid monster?
With over 11,000 retweets and almost 40,000 favorites over the span of two days, the mind-boggling photo has caused meltdowns and double-takes and spawned some truly bizarre photoshop art.
Multiple replies to the post are people who could not figure out what they were looking at. Some beg for answers, others just gave up and admitted it had to be some sort of possessed goat.
In reality, it's a chihuahua who moved its head too quickly while a photo was being taken. Those who figured it out were extremely relieved.
Luckily, someone posted a handy visual too.
Optical illusions come from eyes playing tricks on the brain and the brain's tendency to jump to conclusions quickly. A popular theory is that the brain will try to make predictions of what will happen next in order to make up for the lag time between when a person looks at something and then fully perceives and understands it. That's why sometimes it doesn't make any sense — like looking at what appears to be a goat-horse-dog hybrid on Twitter.