I can't tell you the number of people who tell me they know when their dog has done something naughty because he gives them the "guilty look." As much as I try to convince them that it's just not true, they don't believe me.
A great new research study finds that "people see ‘guilt’ in a dog’s body language when they believe the dog has done something it shouldn’t have – even if the dog is in fact completely innocent of any offense." This is a great read, you can find the rest of the article at Science Daily.