The problem was the cats in the prison recreation hall.

When Percy Jennings, newly assigned to C-block (which contained a petty brand of criminals generally scheduled for release in 3-5 years), first learned this fact, he actually scoffed.

“We have 127 mutinous prisoners and you’re telling me to watch out for the cats?” he bawled indignantly to Brutus, the impassive 6’5” guard never seen without a toothpick. Except on this occasion, Brutus didn’t look quite so impassive, and the toothpick was sticking out of his heavily muscled bicep like a pin on a voodoo doll. Brutus scowled thunderously at Percy, plucking out the tooth pick, (now dyed red almost to the tip), and replacing it to its customary position between his square, yellow-stained teeth. Percy saw that two were missing.

“Mr. Jennings,” growled the prison guard, bending to look Cedric in the face, “Do I look like the sort of guy to kid around?”
“N-no sir,” Percy managed.
“Well then,” Brutus scowled, “if I tell you to watch out for those cats… you watch out for those cats. If you think some scared purse-snatcher is the real threat around here, you’ll be dead meat before you know it. Those cats are the children of the devil.” His breath smelled of peppermint and rotting meat. He stumped away, brushing one of the dangling yellow lamps that lit the concrete walkway between the two opposing rows of cells with his squat, shaven head. Percy suddenly noticed that the prisoners were unnaturally quiet.
“What’s with you lot?” He hollered, and then wished he hadn’t been quite so loud. The sound of his embarrassingly high voice ricocheted along the long, dimly-lit corridor, warped by space and becoming another sound altogether-- A thin wail that raised the hairs on the back of Percy’s neck. It almost sounded like a caterwaul. And the prisoners were silent.
“Strange…” mumbled Percy, making sure to keep his voice down this time. Gingerly, he tiptoed over to one of the cells and peered into the gloom. “Hello?” he called. “Stanley?” The slumped form in the corner did not move. Water dripped somewhere. Percy could hear his own breath.
Then, with shocking speed, the convict raised his head. His eyes shone green. “Behind you,” he hissed. Percy spun around, his heart leaping in his chest. There was nothing there but the empty corridor, the rows of barred cells, glistening yellow in the light of the hanging lamps. Or was there something? A shadow moved at the end… A long curling shadow, a slight, slender shadow…a shadow in the shape of a cat. Percy felt sweat drip into his eyes. He backed up slowly down the corridor, slippery fingers just brushing the cells on the right side. Clawed hands scratched through the bars, reaching for him, but Percy didn’t notice. His eyes were on the cat walking down the corridor in the barred light of the hanging lamps, a black cat with smiling white teeth and green eyes. “Problem,” said Percy Jennings. “Problem”
And teeth sank into his ankles and dragged him back into the darkness of the recreation hall. “You will be the most delicious meal,” said the cat with the green green eyes.
The problem was the cats in the prison recreation hall.