How to fake a giant rat (and why you shouldn't trust pictures on the internet)

A man in London has claimed to have found a rat bigger than a small dog and a cat put together – but all is probably not what it seems.

You know how it goes by now: up pops a picture of someone holding a rat at arm’s length, while a headline blazes something along the lines of: “LOOK AT THIS GIANT RAT!”.

Friday saw the latest instalment in this tabloid trope with the tale of a giant rat in Hackney estimated as “the size of a small child”.

Gas engineer Tony Smith is quoted as saying: “This is the largest rat I’ve ever seen in my entire life. I’ve got a cat and a Jack Russell and it was bigger than both of those put together. I’d say it was about four foot.”

But what actually seems to be going on is a little trick called forced perspective, using an optical illusion to make an object closer to the camera look much bigger. Like the Hackney Rat.

In fact, you too can try and make your own giant rat photo.

With the help of a cuddly toy fox, a selfie stick and our social and new formats editor Martin Belam, we attempted to make it look like we had found a gigantic orange fox with a purple mask in the Guardian offices.

Here’s Martin looking unhappy about being asked to model for us, with the fox looking distinctly not gigantic:

And here he is recreating a similar pose employed in the “monster rat” photos:

People on Twitter were quick to make the same point:

As in the above photo, the rat is much closer to the camera than the man holding it, making it appear absolutely huge. Perhaps it was the biggest rat he had ever seen; but it may not have been “as big as a four-year-old boy”.

Oliver O’Brien, senior researcher and data scientist at UCL, actually did the maths, reckoning the rat was only about two-feet long at best:

He told the Guardian the man in the picture would have to be 12-ft tall if he really was holding a four-foot rat.

He added: “I did two adjustments for perspective – man to right hand, by comparing finger lengths, and then hand to rat – by looking at the parallel lines of the grabber. I also assumed the man was six-foot tall and has equal hands. Very ‘back of the envelope’, but I think my measurements are in the right ball park.”

Hackney Council also weighed in with their own sceptical take:

The picture and story were provided by news agency SWNS. When we asked them about the photo, they said the stated size was based only on the statement from Smith and “clearly perspective plays a part in it”.

That didn’t stop everyone from Sky News to the Daily Mirror to the Evening Standard reporting the story without stopping to ask whether the rat really was four-foot long, or indeed, trying to check the facts themselves.

So the next time you see a picture of a “monster rat” in the news or in your Facebook feed, take a closer look at whether you’re being fooled by an optical illusion.