Of Capture and Torment: Failure

The creature snarls, thrashing against its restraints. Its tattered wings spread wide in a show of dominance, though they tremble with the effort. The chains that hold it rattle loudly, echoing throughout the cell. The dim light reflects off of glistening, scarred skin, a long tail hitting the wall. The sounds prompt a wince from one of the guards in charge of containing it, who speaks quietly to his fellow guard.
"...why are we even guarding this thing? If it gets out, we're dead."
The other guard tenses up.
"Look. Don't think about it too much, okay? It's not getting free. They bound it with the strongest spells our mages can use, we're just for show."
Despite his reassuring words, he too glances nervously at the creature. It's huge, twice the size of a man with wings as long as he is tall. Ragged pink membrane hands from those massive bones like ancient banners, a symbol of times long gone. A savage roar shakes the soldiers to their core. That's the sound of something that shouldn't be contained, something that CAN'T be contained. But there's an undeniable intelligence in its eyes, too. This isn't just some bloodthirsty beast they've captured.
But the guards have a job. The stand by the door of the cell, trying to ignore the sounds coming from within. Each screech of claws on the floor makes them want to cringe, each desperate snarl tightening their chests. It's safe to say that they're quite happy when the mages return.
They say nothing, merely entering the cell and staring down at the dragon-like creature. All of a sudden, the rage the guards had grown accustomed to from the captive was gone. It backs itself into a corner, broken wings folding in as it tries to make itself as small as possible.
"....it's... scared."
The soft murmur leaves the first guard's mouth, though he doesn't seem to have realized he spoke. It's strange to see such an aggressive being suddenly act in what seems to be primal terror. 
Even the mages seem confused, though there's a concerningly eager glint in the eyes of the one in the middle. His black robes cover his face, but a slight smile can be seen on his shadowed features. He stretches out a hand, and the bound creature lets out a pathetic whimper. Its eyes are wide in fear, pupils constricted nearly to disappearing.
The guards are sent away.

When they return, they're greeted with a sorry sight. The chains on the captive's legs have been removed, replaced with a metal collar on a shorter chain than the previous. A black, blood-like fluid drips from its damaged cheek, like an old wound reopened. Those previously piercing eyes are dull and flat, meeting those of the guards for a moment before closing. The guards spend all day standing outside, unnerved by the silence. They leave at the end of the day, relieved by the night watch.

The next day, it's gone. And laying in the shattered collar are two small, white feathers.