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When Luis Suarez appeared to bite Giorgio Chiellini in the World Cup qualifier between Uruguay and Italy, the world stood shocked.

Partly because it wasn't the first time Luis had been accused of biting another player on the pitch.

But mostly because Luis is 27. A grown man.

Yes he's a professional footballer. Yes he should be a role model to the children who look up to him for his world class skills.

But surely a 27 year old man simply shouldn't have the urge to bite someone?

Why did it he do it? Professor Peter Kinderman, clinical psychologist at the University of Liverpool, shared his thoughts on what might cause a grown man to bite someone:

It's not necessarily obsessive behaviour.

Professor Kinderman says: "It’s wrong to assume that people always do things because of an obsession or fetish - even though Suarez has done this more than once, we can’t assume that he has a desire to go around biting people in every day life."

The pressure of the game may have been a factor.

"These 'biting' incidents have happened when Suarez has been full of adrenalin and completely focused on winning. Of course biting is very unusual but we're all capable of doing stupid things when we're under pressure and not thinking straight," says Professor Kinderman.

In pictures - How the biting incident unfolded:

Stress can cause repetitive behaviour.

Professor Kinderman says: "Tennis players throw rackets, some footballers are known for kicking people. Away from sports you get people who, when they're drunk and upset, will lash out at someone or something. Likewise, when Suarez gets frustrated on the pitch, he reacts in the way he has done before."

He needs to engage his brain.

"These incidents have occurred when Suarez has got a lot of pressure on him, he's pumped up, and that doesn't give him any brain power left to restrain his behaviour. He's basically switched off his brain temporarily," says Professor Kinderman.

He can learn to stop.

"People do manage to withhold their impulses, even when they're under the most tremendous pressure. When soldiers are on the front line they are under a huge amount of stress, but if they were to react unpredictably it could prove fatal for themselves and their comrades. They don't, because they have been trained not to react in that way - it is possible to control your urges," Professor Kinderman says.

But first he needs to face facts.

Professor Kinderman says: "The difficulty is, when Suarez is in the middle of an adrenalin fuelled moment on the pitch, his desire to lash out will be at its strongest. If he wants to prevent this from happening again, he would have to accept that he's got a problem that needs addressing and then perhaps work with a therapist to learn how to think before he acts."

More on this:

Luis Suarez 'bites' Giorgio Chiellini - how the world reacted

James Pearce comment:Suarez a deeply flawed genius in need of help

Suarez plays downs claims he bit Giorgio Chiellini but likely to face hefty international ban

Watch: Luis Suarez could face FIFA ban after appearing to bite Italy defender Giorgio Chiellini

Suarez needs help according to Everton boss Roberto Martinez

FIFA will throw book at Suarez says Liverpool legend Jan Molby

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