My old cat Precious (about 13 yrs) has a hairball problem. Well, I bought her different hairball foods and finally found one that work pretty well. But every once in a while when she does throw up (not hairballs anymore) she runs straight for her cat food and eats. I was wondering why she does this. I feed her dry food (Perina Cat Chow) and every now and then canned food (nine lives). I have even taken her to the vet and they checked her for digestive problems. She is very healthy. what would cause her to do this? Thanks.