I don't think it has anything to do with the death of your other dog. He might actually have something in his mouth, have you checked? He could be losing a tooth, or a sore in his mouth that's causing him discomfort. I would try and check it out, take him to the vet if you can. But he could also just be thirsty. I recommend you Mouth ulcer cure through this you get instant of knowledge about how mouth ulcer relief .