While dogs obviously cannot talk, they can communicate. The key as a dog owner is to recognize what the dog is telling you. The dog's behavior shows when a dog is happy or sad, and when the dog is sick. Lethargy, for example, is a telltale sign of a sick dog.
Instructions
Look for stomach ailments. Stomach ailments manifest themselves in a combination of four ways. First, if the dog has diarrhea, like a human, it likely suffers from a stomach ache. Second, if the dog is constipated, it may have eaten something that it should not have. Third, if the dog vomits, then it is likely that it has eaten something that it should not have. Lastly, if the dog's appetite changes, it may be a sign that the dog is sick. If any of these symptoms occur and last for a period of days, then the dog should be taken to the veterinarian.
Assess the movement of the dog. A dog that has been injured or that suffers from a physical ailment like arthritis often will move with a limp or will otherwise have impaired movement. In either case, the dog should be taken to the veterinarian. The veterinarian may be able to treat the injury or offer medication for ailments like arthritis that will make the dog more comfortable and mobile.
Check the dog's breathing. If a dog struggles to breathe, it may be choking, suffering a respiratory illness, or may have an injury affecting the ability to breathe. These issues should be addressed by a veternarian.