It is usually quite easy to tell a psychopath by the blood stained overalls but by the every nature that they can be falsely charming and friendly, they can also slip under the radar until you find yourself stuck up on a hook in an abandoned warehouse while a man with a chainsaw walks towards you and kicking yourself for not realising sooner.
So how can you tell if that work colleague is offering you his stapler out the kindness of his or her heart and not just looking for a reason to return for it later when the office is quiet and lock you in the officer fridge.
Fortunately Austrian scientists have managed to alleviate that little problem by discovering that psychopaths drink black coffee and the stronger the brew, the more psychopathic tendencies the maniac has.
The Innsbruck University tested 1000 people on their food preferences and then asked them to complete four personality tests and the result suggested that 'bitter taste preferences such as Black Coffee are linked to malevolent personality traits'.
So if that colleague with the stapler is clutching a mug of weak tea you should be okay but if it's a black cup of coffee, politely decline and use a paper clip instead.