Oh that makes sense then, because I couldn't believe I wouldn't have noticed it right away. Do they usually go away? I've heard about dogs that have to have surgery to remove it.luv4mygirls said:sometimes the lump doesn't appear for a week after. they were common phone calls at the animal hospital "mysterious lumps" and when we would check the records they had a vaccine within 2 weeks of the lump appearing and it was in that very spot the shot was given.