If you've ever lain down in a field and imagined the clouds were faces in the sky then you'll know what we're talking about. Deliberate optical illusions are one thing, but stumbling across accidental ones is even better! Why? Because it's often a question of individual perception - you may be busy doing double takes, whilst other people won't have a clue what you're so excited about...
Have a browse through these 22 photos WITHOUT reading the titles and then ask your friends what they see...
1. Invasion of the alien zucchini
2. Embracing buildings
3. A heavenly scene or the reflection of a charger on a sofa?
4. When you find yourself following a Sesame Street truck
5. Spot the dog!
6. When four friends watch their pal trying a virtual reality mask for the first time...
7. A bathtub that watches you whilst you soak... complete with gawping mouth and stubbly beard!
8. Parrots or tropical fruits?
9. Because Scrat from Ice Age crops up all over the place
10. When knobbly knees look like babies' faces
11. Meaty sneakers!
12. When you discover Woody Harrelson hiding in someone's belly
13. Ever felt like you're being secretly watched?
14. The Sorting Hat found a new job after his starring role in the Harry Potter movies
15. There's a reason this kitty's called 'Excalibur'
16. When a tree decides to sit down and rest
17. A swing for mini-Ninja Turtles
18. When you find a Stormtrooper lurking amongst the dishes
19. Fancy sampling a cocktail that has a murdered olive floating around?
20. When Patrick Stewart takes a nap in your pile of laundry
Bonus: Bird poop that looks like a bird!!!
A woman with ridiculously long thighs or just an interesting angle?