She's got a WHAT?

Ray was howling at the door as Moonie and I got in the car and pulled out of the driveway. I had found it necessary to close him up in the dining room while I slipped the cat into her carrier. I was familiar with the drill because it happens whenever I take Moonie to the vet. The minute I bring the carrier inside, Ray gets anxious and jogs nervously around the house while I snag the cat and put her into the travel device. When Moonie starts yowling, Ray whines. When we leave the house, he howls and scratches frantically at the door. I'm not sure what his thought process is, I can't tell if he is worried I won't bring her back, or if he wants to go with her, but it really upsets him when I take his cat away.
I had found a lump on Moonie's abdomen the previous evening when I was giving her a bellyrub. I was pretty sure that it hadn't been there the night before that, and I was very concerned that it might be a tumor of some kind. So we were on our way to see the vet.
It was snowing, so I threw a blanket over Moonie's cage to keep the cold air off of her. As usual, she meowed the whole way there but became quiet when we arrived. We didn't have to wait for long.
"Her weight is maintaining," said Dr. Kim as she looked at Moonie's chart, "That's good. Where is the lump that you felt?"
The vet was running her hands over Moonie's belly as she asked me the question. Her hands stopped and she looked at me.
"Is this what you felt?" she asked.
I reached under Moonie, felt the lump, and nodded.
Dr. Kim said, "It's a hernia."
"Huh?" I said, thinking I had misunderstood.
"It's a hernia," repeated the vet, "Usually kittens have them. I've never seen one on an old cat like this."
"As far as I know she hasn't been moving furniture or anything," I said, "How would she get it?"
"I have no idea," replied the vet.
She told me to monitor it to make sure it doesn't get bigger and told me what great shape Moonie is in for an old cat with kidney disease. Moonie sat on the table and purred. I opened up her cage and the old cat spryly scooted in, ready to go home.
Ray met us at the door happy to have his cat home safely, then ran upstairs to tell Hugo that his sister was home.