Tossing a coin needn't be random at all, according to research.
A study at the University of British Columbia found that it's actually pretty easy to manipulate, with a little training.
Thirteen otolaryngology residents were asked to toss a coin 300 times each with the aim of turning up heads. All participants managed more heads than tails, and more than half achieved significantly more.
The best performer - who may have better future prospects as a trickster than a doctor - managed nearly seven heads out of ten.
"This study shows that when participants are given simple instructions about how to manipulate the toss of a coin and only a few minutes to practise this technique, more than half can significantly manipulate the outcome," say the authors.
"With devoted training, more participants would probably be able to achieve this figure, and the magnitude of the manipulation would probably be increased."
When the Euro was first introduced, Polish statisticians claimed that the Belgian 1 coin came up heads more often than tails. This resulted in a tongue-in-cheek warning in the British press to teams playing against Belgium in the soccer World Cup.
The study does have some medical relevance, as coin tossing is still used as a method of randomisation in some trials.
It would also indicate that next time you get into a duel, you should toss the coin yourself rather than let your opponent do it.