When he had not improved after two weeks, the Johnsons took him to the University of Pennsylvania's Matthew J. Ryan Veterinary Hospital. An abdominal ultrasound and other tests turned up nothing unusual.
Since slow chewing was the only identifiable sign of a problem, the veterinarians pinned Zeb's problems on the gastrointestinal system. They recommended changes in diet and the tincture of time, and sent him home.
Then Zeb became reluctant to walk.
"I knew my cat," said Ricki Johnson, "and I knew something was seriously wrong."
Back at their regular vet, a physical exam elicited neck pain. X-rays were normal. Put on corticosteroids for inflammation, Zeb improved over the next two weeks, but again resisted walking.
They returned to Penn in November 2012. Now eight weeks after his first symptoms were spotted, Zeb appeared to be less aware of his surroundings and was uncoordinated when pressed to walk, falling to the right. His right eye appeared sunken.
The vet laid him on his back; his eyes darted up and down.
Rapid eye movements in a cat are a sign of nerve problems. Involuntary darting from side to side may indicate a peripheral neuropathy, perhaps caused by an inner-ear infection. Rhythmic up-and-down movement like Zeb's, called vertical nystagmus, suggests something in the brain.
An MRI of Zeb's brain revealed a large tumor over the right cerebral hemisphere. The meningioma was two centimeters in diameter - half the size of his brain.
"You could imagine that a lot of those signs he was showing might have been from a really bad headache," said Zeb's veterinary neurologist, Evelyn Galban.
Meningiomas arise not from brain matter itself but from the meninges, the membranes covering the brain. They are the most common primary brain tumors of cats and dogs. Older animals are more prone to develop them, on average around age 12 in cats and 9 in dogs. The tumor's growth compresses brain tissue, leading to the onset of clinical signs.
In cats, which typically are brought in with changes in mental acuity, vision, and gait, meningiomas are usually benign and well-encapsulated. Surgery is the treatment of choice. Dogs' most apparent symptoms are more likely to be seizures, and the tumors tend to be more invasive and often malignant; surgery is trickier, and the prognosis is poor.
People also get meningiomas; the vast majority are benign but surgical options depend on where the tumor is located. There are no good chemotherapies, although radiation can prolong survival in all three species.
After much deliberation, Zeb's owners chose surgery. The Penn surgeons were able to completely excise the tumor, which Galban described as a whorl of mineralized concretions in an onion-bulb pattern, "just like a van Gogh painting."
But Zeb experienced complications overnight, and his limbs became rigid. He was given the drugs mannitol to lower increased intracranial pressure and phenobarbital to prevent seizures. He improved and was discharged after six days, free of clinical signs.
Even when they are completely removed, meningiomas regrow about a quarter of the time in cats.
Nearly two years after surgery, Zeb shows no signs of regrowth. He remains on phenobarbital because of a few seizurelike episodes, but his prognosis for a full nine lives is excellent.
Joan Capuzzi is a veterinarian at Cottman Animal Hospital in Northeast Philadelphia. email@example.com.