My dog, not long before he died, had a decent sized ulcer on his skin. I had him at the vet the Saturday before he ended up in the hospital and they didn't find it. I found the ulcer on the following Monday or Tuesday. He had been acting weird before the vets visit and it continued. The vet on Saturday assumed it was just his Addisons Disease acting up. When I took him in to the ER, the ulcer was infected. He went downhill overnight, unrelated to the ulcer and the next day he was gone.