That "guilty look" on a dog's face is all in the imagination of the human owner, suggests research.
Dog owners have often claimed they can read the expressions of their pets - particularly that tell-tale look when they have done something wrong.
Some even maintain that they can tell the exact nature of their dog's crime as soon as they see their faces.
Margaret Green 56 from Acton in West London told Science correspondent Jane Lister:
"I know from the moment I walk through the door whether Dylan (a liver coloured Springer Spaniel) has been a good boy or not. His expression is so full of guilt and I know he is feeling bad about his behaviour. The other day he gave me one of his looks and I spent over three hours searching the house to see what he had done. I could not find anything smashed or out of place. It was only when my husband suggested that I checked the outgoing telephone calls that I realised he had been ringing live 1-2-1 adult chat lines all morning. He must have been doing it a lot because the phone bill was astronomical . I was furious and sent him to his basket without this dinner. My husband has promised to keep a closer watch on Dylan next time they are alone in the house together".
But researchers at a New York college tricked owners into thinking innocent pets had misbehaved - with the owners still claiming to see this guilty look.
The study found that the expression had no relation to the dogs' behaviour.
And researchers found that pet owners' belief that they could read their dogs' "body language" was often entirely unfounded.
Not having an affair with his secretary
The study from John McNulty, Professor at Barnard College in New York, showed that owners were projecting human values onto their pets.
"Dog's do not feel emotions in the same way as us humans. If I were to be having an affair with my young secretary, which I am not, I would feel guilt and this could manifest itself in many physical ways, for example through eczema or psoriasis".
"But because I am not having an affair with my secretary I do not have to worry about my skin erupting. I can go home to my wife and three children at the weekend free of guilt because I have always remained faithful".
"Canine lovers often falsely believe that their pets feel emotions in the same way. We actually had a lady who took her dog to confession because she believed he had been overly sexual in the park. More worrying perhaps is the fact that the priest gave the Irish Wolfhound four Our Fathers and five Hail Mary's"
The research, 'Canine Behaviour and Cognition', looked at how dog owners interpreted their pets' expressions, when they believed that the dog had stolen and eaten a forbidden treat.
In a series of tests, owners were sometimes given accurate and sometimes false information about whether their dog had stolen the treat.
But the research, published in Behavioural Processes, found that owners' interpretations of whether their dog looked guilty bore no reliable link with whether the dog had really stolen the treat.
On one of the tests a particularly bright Border collie called 'Dave' fooled his owner into believing he had not eaten the chocolate by sitting cross-legged in an armchair, smoking a pipe and immersing himself in the Daily Telegraph.
However if an owner thought the dog had misbehaved and then subsequently told the dog off, some dogs showed an "admonished" look, which humans then misunderstood as an admission of guilt.
Researchers concluded that any such "guilty look" is a response to human behaviour and has no relation with the dog's actions or sense of having broken any rules.
Sometimes people can look like they are having affairs when they are not.
Interestingly certain breeds of dog seem to look more 'guilty' than others. Bloodhounds, Whippets and Beagles notoriously get blamed for everything whilst Rhodesian Ridgebacks, Rottweilers and Pitbull Terriers tended to get off scot-free no matter what they did.
Professor McNulty concludes: "Like humans some dogs have naturally more guilty looking faces than others. My wife often accuses me of things I haven't done and I'm sure that's because I have similiar features to that of a Bassett hound".