Shapeshifting

For some the ability to change their shape is inherent; changelings, for example.

Others acquire the ability but have no control over it, such as lycanthropes.

And still others simply use magic, or magical aids such as potions, to do so or to inflict shape changing onto others against their will.

The duration of transformations and what one is able to turn themselves (or others) into varies wildly based on many factors. But the point remains; be careful to whom you speak, and what about, as you never know who could be a shapeshifter in disguise.