Reacts to a very quiet sound

He raised himself up to get a better look, glancing cautiously over at the
wagon. To his surprise, the Whaler—the actual Whaler—had gone.
Corvo ducked around a pillar, careful to keep himself in the shadows as
he cast his gaze around the square. The other men continued digging,
oblivious to the fact that their leader had gone—but where?
He had a good view of the wagon, and the Whaler wasn’t anywhere near
it. He wasn’t walking back toward the cemetery gates either. There was
plenty of cover beyond, but the space between the gates and the wagon was
open and well lit by the moon.
There was a sound from behind Corvo.
Infinitesimally small.
A tick, a click, metal on metal.
The sound of a switchblade.
Corvo spun around. Impossibly, the Whaler was standing behind him on
the balcony, knife in one hand, the other outstretched, fingers splayed.