According to scientists, that sweet, puppy-like look of our dog after bumping into another rubbish bin is not a sign of the feeling of guilt. The dog simply responds to our scolding. When the owner thinks that his dog has just eaten a forbidden treat, he scolds him and the dog looks as if was guilty regardless of whether he has actually eaten the treat or not. In fact, dogs who were wrongfully accused of stealing the treat very often look even more guilty than those that have really taken it. After all, as it seems, these sad eyes do not reflect any deeper thinking process.

Source: www.livescience.com