Von Essen, a student at the University of Gothenburg, tried out a few of the techniques – the benefits were instantaneous: “Almost immediately I realised I could memorise more things than I ever dreamed possible,” he says. His first competition was the Swedish memory championship in 2012, which he won. He went on to become world memory champion in 2013 and 2014.

Von Essen uses a slightly different technique to remember cards. He has an image that he associates with each individual card, which he groups into sets of three, before placing them on a short walk through his house. “So I might start at the front door,” he says. “Say it’s the four of hearts, the nine of hearts and the eight of clubs – I’d open the front door and see an image of Sherlock Holmes playing the guitar and eating a hamburger. Then I’d walk into the hall and create a new scene with the next three cards.”

What’s your favourite restaurant?

Memory palaces can be anywhere – hotels, houses, routes to work, restaurants, a favourite holiday, a park or a train ride. “If you sit and think about it for a moment you can come up with hundreds of locations that you know pretty well,” says Mullen.

Both of the world champions use specific mind palaces for things they want to remember in the short term – like a pack of cards – and things they want to remember forever. “So for the five-minute number competition I use the same two palaces, then re-use them the next time,” says Mullen. “Because I don’t want to remember a five-minute event I did two years ago. But when I’m learning things for school, say drugs that treat stomach disorders, I’ll fill up a palace and not use it for anything other than related information.”

‘Does it work every time? Doesn’t your mind ever go blank?’ I asked both competitors. No, was the answer. “If you’ve put it in your mind palace, it’s always safe,” says Von Essen.

Another thing they agree on is that the gift of extraordinary memory is nothing special – anyone can learn how to do it to a fairly decent standard. Mullen trained just half-an-hour to an hour each day in preparation for the World Championships. Von Essen also trained for small amounts of time each day, before gearing up to five hours a day just before competitions.