We all remember the dress. Then there was that banana illusion. But that was mere child's play compared to this, an optical trick which can alter the way your brain works for up to three and a half months.
So think carefully before embarking down this path of mind-wreckery. As the video below explains, there exists something called the McCollough effect, which works at the level of the brain itself.
To experience it (don't say we haven't warned you, because we have), you first need to look at the black and white test image, which contains oppositely oriented gratings of lines - horizontal and vertical.
Next up, you need to stare, alternately at the two 'induction' images - the square with horizontal red and black lines, and the square with vertical green and black lines. You need to stare at each image for several seconds at a time, and for a total of several minutes. Stare at the centre of each image but allow the eyes to move around a little.
Once you've had enough, stare back at the test image: the gratings should appear tinted by the opposite colour of the induction gratings: in this case, horizontal will be greenish, and vertical pinkish. It can also work with blue and orange.
The effect can often last an hour or more and, with prolonged exposure (of around 15 minutes), up to three and a half months.
It was originally discovered by American psychologist Celeste McCollough in 1965 and there are three competing explanations for the effect - all we'll say is that it's really weird. Try it for yourself and see.