This is frequently the subject of much confusion. Hairballs (in ferrets or cats) cannot be passed by use of any oil that is absorbed by the intestinal tract. That includes ferretone, corn oil, olive oil, etc. Although they may be good for the ferret, they do nothing for hairballs. In order to help pass hairballs, you must use a NON-absorbed type of "grease" like laxatone or other remedy designed for that. All those products are basically vaseline, and since they are not absorbed in the intestinal tract, they pull the hair out as they pass. Please don't use mineral oil. It will technically do the job, but it's way too easy for an animal to aspirate it if it's being squirted in the mouth. Mineral oil in the lungs stays forever, and does not do good things. Dr. K. [Posted in FML issue 2448]