Emperor

An evil emperor in a fantasy world with an enormous aviary full of exotic birds that are exceptionally well cared for. They are friendly and not territorial species from a distant enough land that very few people in the kingdom that knew much about them. They are moderately intelligent but, crucially, not able to imitate sounds or speech, but they are very trainable and curious. Occasionally importing new birds for their aviary would be the emperor's big frivolous indulgence that their politic enemies would make fun of.

They also have a sorcerer in their employ. When a hero or a renegade or a political rival is in a situation where the emperor can safely kill them, they will instead be turned into a bird and added to their aviary. They would not brag about this; it would be a complete secret known only to them and their sorcerer. In situations where they capture multiple people working together, only one would go in the aviary; the others could be imprisoned or executed or whatever. If they escape and the emperor reacquires them later, another one can go in the aviary. The point is that nobody going in the aviary can safely assume that another bird in there is their teammate.

Because the emperor would be trickling real birds in there too, and would train some of them to do 'intelligent' things like tap out prime numbers or scratch shapes into the dirt with their beaks. They would train some of them to pick at the locks and bars as if they were trying to escape. They would not train them all the same way, or train many of them at all.

Sometimes a new bird goes into the aviary -- fellow revolutionary? Or just another bird? Is it trying to communicate to you that it's human, or just being friendly and imitating you because that's what smart, friendly birds do? People would develop opinions and theories over time. They'd amass in a group of the smartest ones, pretty sure that they're closest four or five friends are humans, are using their invented little language of wing flaps and trills with a human mind behind it... but can they ever really be sure?

Most people, when going into the aviary, would assume that all of the birds are captured enemies. So why are some of them hard to have ongoing communication with, to learn about, to plan with? Are these the natural communication barriers of someone in a bird body, or does being a bird make them stupider over time? Will that happen to them also?

Sometimes, if the emperor captures a pair, they'll imprison them separately, then turn one into a bird and put them in the aviary at the same time as a real bird that's trained to have a couple of their partner's mannerisms.

When they interact with the birds, even in private, they won't secretly mock them or make clever veiled references to their past lives or act at all like they remember that they were once human. They are their birds, that they imported at great expense. And they've brought a treat for them: some fresh fruit, and another friend to share it with! A new bird!

Or is it?