Pixel saw the vet yesterday. His gums are inflamed. I didn't notice that, but then, I didn't think to check. His gums on the left side are swollen and real red, so the vet thinks it hurts to eat. He said it might be an autoimmune disorder, did a blood test, and gave him 2 antibiotic injections, one in each shoulder. The blood test ruled out leukemia as the cause.
Vet said Pixel might have an ulcer in his throat, too, but the antibiotics will help with that.
We go back in 2 weeks. Meantime, he wants me to keep giving Pixel soupy canned food* but start introducing a little bit of it straight-from-the can in a few days; like, put down a bowl with a tablespoon or two of regular canned stuff next to his bowl of soupy stuff. When his mouth feels better, he'll eat the regular stuff. Then I can try kibble soaked in warm water, and so on.
*for over a month now, he'll only eat canned food "soup" - I stir in plenty of water, squish all the chunks with the back of a spoon, and then strain out any little hard bits.
I'm amazed at the amount of what looked like tiny bone shards in canned catfood. Except for salmon. The salmon flavored ones didn't have any bone shards, or whatever those were. Could have been bits of plastic for all I know. I also found lots of what appears to be tiny bits of fiber, like cotton or wool or something.