The below tweet from Kyle Hill got us thinking.
There are only four circles here and they don't touch. C'mon brain you can do this. pic.twitter.com/mDPLXwl9av— Kyle Hill (@Sci_Phile) December 19, 2014
No, not thinking 'why does my brain hurt so much', but about some of our other favourite optical illusions. Let's get right to it.
The dinosaurs aren't actually moving
Skip to the 1:30 mark to see how it was done.
These circles aren't moving either
It's thought the way our eyes repeatedly scan images is behind the illusion.
Spotting a trend? This is a static image, not a gif
The two squares marked A and B are the same colour
Take another look at this elephant's legs
Sometimes our brain fills in the gaps when we expect to see something - even if it actually isn't there.
The disappearing chocolate bar
Here's how this one was done.
The circle in the middle is not changing size
This took first prize in this year's Illusion of the Year contest.
These roads will really mess with your head
Stare at this heart - notice anything unusual?
This should definitely have been an emo band album cover.
You'll never look at Pac-man the same way...
More: [The nine optical illusions that will make your brain melt]5