In the world of the gentleman bastard sequence work animals are often 'gentled' using a substance called wraithstone. Gentled animals are mindless and show no emotion or care. "
"Wraithstone smoke poisons nothing physical; what it does is burn out personality itself.
Ambition, stobornness, pluck, spirit, drive." (LoL)
They are described as empty shells. These animals are good for working in over crowded cities. Gentled animals show no fear for their lives and are therefore very easy to kill.
To gentle a sack is placed over the animals muzzle with a piece of Wrathstone and a slow burning match. At one point in the past wraithstones were used on human criminals but is only used on animals in the time of the books.
In the Lies of Locke Lamora Capa Raza attempts to gentle the nobility at the Duke's annual party.