Can dogs eat eggshell

Dogs can pretty much eat anything. The real question is: WHY would you feed your dog egg shells? Note from omigodlucy; The reason I ask this question is because my uncle, who is a veterinarian, insists that egg shells provide an Excellent (and free!) source of protein for dogs. My concern is that they might be dangerous, particularly for younger puppies, because they may be difficult to digest and/or the sharp edges may damage the dog's oesophagus. My apologies, I should have made my question a little more clear. Thank you for your response.