Mind-bending optical illusion tests your eyes – can you work out what is going on with this bird with ‘face of a seal’?

A MIND-BENDING optical illusion has appeared in the sky - with people baffled over a bird appearing to have the face of a SEAL.

The unusual photos capture a swift, which looks swollen as it stuffs its face with hundreds of insects.

It was spotted feasting while flying in Tices Meadow Nature Reserve in Farnham, Surrey.

Photographer Jon Hawkins, 60, explained that swifts, which can reach speeds of almost 70mph, can collect more than 1,000 insects in a pouch in its throat at one time.

The bugs are bound together by saliva and this is called a bolus, which causes the bird's facial appearance to appear distorted.

Its catch can then be regurgitated and fed to chicks.

Jon, who is based in Ash, Surrey, said: "The call of the swift as they gather in numbers to feed is known as a ’screaming party’ and it sounds like a warbled screech.

"Swifts spend ten months of the year in flight - eating, drinking, sleeping and even mating on the wing, only landing to nest.

"Some juveniles won’t land for two years after fledging, so you never see them perched anywhere apart from on a nest.

"I think the swift looks like either a seal with wings or a bird with a bulldog's head.

"I like that the images show something that is not visible to the naked eye as they are moving so fast."

Other incredible optical illusions include this image where a heart is hiding among elephants.

And you could be a record-holder if you manage to find it in under 20 seconds.

And another illusions is said to reveal how your brain can lie to you.

The trick makes us perceive a black-and-white image in colour.

Meanwhile this optical illusion will tell you just how dirty your mind is.