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This goose has clearly decided to fly upside down. But why?

Photographer Vincent Cornelissen took the picture of the dark grey-brown Bean goose flying near the town of Arnhem, in the Netherlands.

The picture shows the goose with its body upside down, twisting its neck and head around to its normal position. We're reliably informed the goose is fine, however, it may be a bit of a whiffler.

Speaking to Newsround, Cornelissen said he was surprised by what he saw and hasn't seen a goose flip over before or again since.

"I go out almost twice a week and never saw it. Even now that I know of this behaviour I look at them fly regularly, I never saw them do it again," he said.

"I was absolutely surprised! I never knew a goose was capable of doing this. First I thought it flipped over because of the wind."

But... why is that bird doing that?

After the picture went viral on Twitter, experts guessed what the bird might be doing, including 'showing off' or flipping over as a way to slow itself down while flying.

"They told me it's called "whiffling'," says Cornelissen, explaining the unusual method of a bird slowing down.

"A professor of the University of Istanbul told me he believes in the whiffling theory because the turning causes down-force on the wings. He even uses this picture in his lessons.

"A bird professional in the Netherlands says it's probably a way of showing off to his fellow geese. I don't know what is true, I like both explanations."

Is it real?

However, some people on social media have also said they think the image is fake, something that Vincent can understand.

"There are still a lot of people who think this is fake and I can understand that. It's something that not many people know of or have seen.

"I have no need to defend myself," he added "It is what you see and although it's rare, there are people who knew about this behaviour. I always try to comment when people have questions about it and often show them the pictures i took."

The picture was actually taken and shared on social media last March, but has recently gone viral for a second time thanks to a photography competition in Cornelissen's home country of the Netherlands.

"I'm honoured that I get so many positive reactions and that the picture puts a smile on many faces. It's a picture that people share and talk about with each other. I'm thankful that I was there on that rainy and windy day in Arnhem back in March," he said.