They were everywhere online as hugely popular images asked you to spot the odd figure out everywhere you turned on social networks.
The Neural Correlate Society runs a yearly contest for the best optical illusion of the year.
Here are a selection of the best from this year:
Researchers from the University of Nevada Reno came up with this entry, which is based around moving dots which make a square.
Except they aren't moving and that's the bit that will really mess with your head.
It's hard to explain - take a look for yourself.
This one is called the ambiguous cylinder illusion and it's going to wrinkle your brain.
If you see squares at the top of the cylinder, the mirror will show you cirlcles, and vice versa.
It's the creation of Kokichi Sugihara of Meji University, Japan, whom we assume is a bloody sorcerer.
It appears to be done with angles and the fact the cyclinder has an uneven top rather than a flat top.
This video will explain:
This is essentially an inversion of the typical Zoetrope of the Victorian era.
The silhouette of the bird comes to life with a strobe effect.
This illusion, by Mark Vergeer, Stuart Anstis and Rob van Lier of the Universities of Leuven, Nijmegen and UC San Diego, will make the grey bubbles you focus on turn colourful.
This is because each bubble with essentially "capture" the colour of the correlating bullseye.
The video will explain better than I can.
You'll need a partner for this one and some bare elbows.
Not sure what we're talking about? Lets explain.
This illusion is tactile and concerns our sensory anticipation. You're likely to not know where your elbow is if told to say "stop" when you have your eyes closed and someone runs their finger up the inside of your arm.
If two rectangles flash at the same time your eyes will see them as doing so simultaneously.
You can, as Arthur G. Shapire of American University does gleefully in this video, mess with the surrounding context to trick them into thinking they're out of sync.
It has ruined our eyes.
The hidden mobile phone illusion from earlier in the ear absolutely broke the internet, for obvious reasons.
The blue and green colours in this spiral are actually exactly the same.
Don't believe us?
This one is by Akiyoshi Kitaoka, a professor of psychology specialising in visual perception at Ritsumeikan University in Kyoto, Japan.