Often optical illusions are made for fun ... She pounced right in and asked viewers to "stare at the black dot in the centre of the rainbow". She added: "Keep looking at it, count for 15 seconds." ...

Brainteasers are a delightful way to challenge your wits – and optical illusions can work wonders ... she invites viewers to ...

But how different do things look if you’re colour blind? In a video created by the BBC back in 1985, an optical illusion featuring the Union flag was created to educate people on how colour blindness ...