The viral clip left people feeling delirious as they struggled to determine what exactly was going on.

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Mum Shannon Brown heard “through word of mouth” about the local marvel mystifying residents in Ontario, Canada.

She decided to hop in her car and take her daughter to see the incredible illusion in the town of Port Colborne.

The pair drove along the lakeshore heading east to see the spectacle that has flummoxed Canadians for decades.

They filmed their journey along the road, showing them heading towards a federal grain elevator mill in the distance.

As they approached the building which is cloaked by a veil of trees, the mother and daughter duo realised it seemed to be significantly smaller than when they first spotted it.

Stunned Shannon can be heard saying: ” It’s getting smaller… why was that building so big? Why is it so small?”

They continued to travel along the road, before reaching a bend instead of arriving at the mill like viewers presumed.

Social media users could hardly believe their eyes when the structure, separated from Shannon by the sea, seemed tiny -when minutes earlier it had appeared to be massive.

Even Shannon’s youngster was perplexed by the extraordinary ‘shrinking mill’, as she asks: “Why does it do that? Back there it was huge!”

The confused mum responds: “I don’t know! Look how little it is.”

Social media users were also dumbfounded by the real-life optical illusion in Canada.

One wrote: “Maybe they are going slightly uphill?”

Another said: “I don’t like what this just did to my brain.”

And a third chimed in: “Glitch in the matrix.”

But others insisted there was a simple scientific explanation for the eye-popping illusion.

One explained the baffling clip is actually footage of the Ponzo effect – or the Moon Illusion – happening in real time.

The term, coined by Italian psychologist Mario Ponzo, refers to an illusion where two identical lines appear in different sizes due to human perspective.

In this case, the trees and houses lining the street take on the role of Ponzo’s converging lines.

These surroundings distort your perception of the mill and initially trick your brain into believing it is bigger than it really is.

As Shannon continues to drive, more of the surrounding horizon is revealed which prompts your vision to constantly readjust.

This creates the illusion and gives motorists the feeling that the building is steadily shrinking as they get closer.

The Ponzo effect is so powerful that it can even be captured on video.

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