One, somewhat humbling, explanation is that we are all “cognitive misers” – to save time and energy, our brains use intuition rather than analysis.

As a simple example, quickly answer the following questions:

“How many animals of each kind did Moses take on the Ark?”

“Margaret Thatcher was the president of what country?”

Between 10 and 50% of study participants presented with these questions fail to notice that it was Noah, not Moses, who built the Ark, and that Margaret Thatcher was the prime minster, not the president – even when they have been explicitly asked to note inaccuracies.

Known as the “Moses illusion”, this absentmindedness illustrates just how easily we miss the details of a statement, favouring the general gist in place of the specifics. Instead, we normally just judge whether it “feels” right or wrong before accepting or rejecting its message. “Even when we ‘know’ we should be drawing on facts and evidence, we just draw on feelings,” says Eryn Newman at the University of Southern California, whose forthcoming paper summarises the latest research on misinformation.

Based on the research to date, Newman suggests our gut reactions swivel around just five simple questions:

Does a fact come from a credible source?

Do others believe it?

Is there plenty of evidence to support it?

Is it compatible with what I believe?

Does it tell a good story?

Crucially, our responses to each of these points can be swayed by frivolous, extraneous, details that have nothing to do with the truth.

Consider the questions of whether others believe a statement or not, and whether the source is credible. We tend to trust people who are familiar to us, meaning that the more we see a talking head, the more we will begrudgingly start to believe what they say. “The fact that they aren’t an expert won’t even come into our judgement of the truth,” says Newman. What’s more, we fail to keep count of the number of people supporting a view; when that talking head repeats their idea on endless news programmes, it creates the illusion that the opinion is more popular and pervasive than it really is. Again, the result is that we tend to accept it as the truth.

Sticky nuggets

Then there’s the “cognitive fluency” of a statement – essentially, whether it tells a good, coherent story that is simple to imagine. “If something feels smooth and easy to process, then our default is to expect things to be true,” says Newman. This is particularly true if a myth easily fits with our expectations. “It has to be sticky – a nugget or soundbite that links to what you know, and reaffirms your beliefs,” agrees Stephan Lewandowsky at the University of Bristol in the UK, whose work has examined the psychology of climate change deniers.

A slick presentation will instantly boost the cognitive fluency of a claim, while raising its believability. In one recent study, Newman presented participants with an article (falsely) saying that a well-known rock singer was dead. The subjects were more likely to believe the claim if the article was presented next to a picture of him, simply because it became easier to bring the singer to mind – boosting the cognitive fluency of the statement. Similarly, writing in an easy-to-read font, or speaking with good enunciation, have been shown to increase cognitive fluency; indeed, Newman has shown that something as seemingly inconsequential as the sound of someone’s name can sway us; the easier it is to pronounce, the more likely we are to accept their judgement.

In light of these discoveries, you can begin to understand why the fear of the flesh-eating bananas was so infectious. For one thing, the chain emails were coming from people you inherently trust – your friends – increasing the credibility of the claim, and making it appear more popular. The concept itself was vivid and easy to picture – it had high cognitive fluency. If you happened to distrust the FDA and the government, the thought of a cover-up would have fitted neatly into your worldview.