There are many reasons your dog may have an upset stomach, though theres one common cause: they ate something they shouldnt have, says Kathy Backus, DVM, at Holistic Veterinary Services in Kaysville, Utah. Dogs are curious like kids; theyre always putting things in their mouth, she says. Vomiting and diarrhea are signs that a dogs body is trying to expel something that shouldnt be in their system. In a healthy dog, its a protective mechanism of the body thats ...