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This optical illusion is so brain-twisting it comes with a health warning.

The trick can make you see black and white as green and red for up to three and a half months.

To make the trick work you have to stare at images of vertical and horizontal lines so that you eventually start to see black and white as green and red.

It's known as The McCollogh effect as it was discovered by an American psychologist in Canada in 1965.

The trick is so effective you should think twice before staring at the images below.

You have to look at images of vertical and horizontal lines so that you eventually start to see black and white as green and red.

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The illusion's effects can last for a long time depending on how long you take part.

It's recommended that you do not carry it out for longer than 15 minutes.

To perform the trick you need to look at the test grid of black and white lines and confirm they do indeed look black and white.

Then you stare alternately at the square containing red and black stripes and the one with green and black stripes for up to three minutes.

Then you look back at the black and white lines once more.

WARNING: May change your perception of colour

At this point, you should be able to make out that the top right and bottom left vertical stripes of the black and white grid are a little pink, whilst the top left and bottom right horizontal stripes should appear slightly green.

The exact reason the trick works is not fully understood.

But the exercise bears some similarity to the blue/black or white/gold dress illusion that caused such a stir back in February.

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