My guinea pig has had a growth on her neck for about four weeks. When she first got it, I took her to the vet who tested it and said it was benign and recommended leaving it if it didn't seem to bother her. It grew to about the size of a kiwi but tonight it exploded with smelly pus. I have given her a bath with the same small pet shampoo that I normally use. I will phone the vet first thing tomorrow but is there anything I can do in the meantime to make sure she is OK? This all happened about 2.5 hours ago, she seems fine now. I am not sure if there is a hole left in her neck or not.