Sometimes the best way to deal with a bully is to look them in the eye, stare them down and show them that you mean business – or at least make them think you do. It’s very similar in the animal kingdom as well, where direct eye contact is a well-established marker of hostile intent for many species both above and below the waves. But what happens when the creature you’re trying to intimidate isn’t a playground bully but a dangerous underwater predator with lots of sharp teeth and a nasty habit of chomping on your fins?

In the turbid rivers of South America, a number of piranha species have discovered that fish fins are a great food source because they’re abundant and rapidly renewable. This poses a big problem for the piranhas’ victims however, because even if they escape being eaten entirely, damaged fins often lead to lethal infections and also make it much harder to feed and escape other predators.

As a result, a number of crafty fish such as Oscars have developed false “eyes” on their fins to warn opportunistic piranhas to back off. Properly known as ocelli, these eyes are no more than circular patterns strategically placed close to their caudal fins and coloured to closely mimic the fish’s real eyes. As a result, even large and slow-moving fish can enjoy a measure of respite from fin-nipping, and it just goes to show that you can even give a fearsome piranha some pause for thought if you make him think you have your eye on him...