My aunt's beloved cat Ginger had grown seriously overweight, so she decided to take him to the vet to find out if there was anything wrong with him - and more to the point, whether anything could be done about it. So she put him into the kitty-carry box, and drove to the surgery.
The doc prescribed a course of pills, and my aunt left, happy in the knowledge that Ginger would soon be his slim old self again. But after a few weeks of taking the pills, there was no change: Ginger was as fat as ever. Soon months had gone by, and still there was no difference. In fact, if anything, it was getting worse. The other problem was the invoices from the vet - these pills were costing a fortune.
It soon became clear to us all that Ginger had become a doc-billed fatty-puss.