The secret, apparently, is to linger on your chosen card as you riffle through the deck. (In our conversation, Olson wouldn’t divulge how he engineers that to happen, but others claim that folding the card very slightly seems to cause it to stick in sight.) Those few extra milliseconds mean that it sticks in the mind, causing the volunteer to pick it when they are pushed for a choice.

As a scientist, Olson’s first task was to formally test his success rate. He already knew he was pretty effective, but the results were truly staggering – Olson managed to direct 103 out of 105 of the participants.

Unsurprisingly, that alone has attracted a fair amount of media attention – but it was the next part of the study that was most surprising to Olson, since it shows us just how easily our mind is manipulated.

For instance, when he questioned the volunteers afterwards, he was shocked to find that 92% of the volunteers had absolutely no idea that they’d been manipulated and felt that they had been in complete control of their decisions. Even more surprisingly, a large proportion went as far as to make up imaginary reasons for their choice. “One person said ‘I chose the 10 of hearts because 10 is high number and I was thinking of hearts before the experiment started’,” says Olson – despite the fact that it was really Olson who’d made the decision.