allhailthevoid:

Legends persist in Überwald of the existence of a malevolent sub-set of normally human-shaped characters who can, at will, transform into the shape of ducks. Opinion is varied as to the efficacy or the usefulness of this ability. Apparently those blessed with this ability become considerably more stupid and agressive, and travelers in remote areas have experienced the dread of passing through a damp area and hearing the ominous quack and the slap of webbed feet behind them. Advice is for them to hurry away and on no account look behind them.

-The Celebrated Discworld Almanak