Snape waits, not moving from where he's standing at the head of the desk, where he can lock eyes with the young man when he looks up.

He waits until his trousers are pushed down, watches the way his slender body shifts to manage it without standing again, hearing the soft sounds of his breathing, huffs that sound so put out. Black silk boxers follow trousers down, and expose the pale skin of his ass and thighs.

The tone of his voice is losing its edge somewhat. The rest will fade soon enough.

He is careful not to be caught staring at the newly exposed skin when Draco looks up at him. Snape keeps his attention and then dismisses it as he begins to move around the desk, around behind Draco, standing slightly left of center.

"You'd do well to keep quiet," he warns, and after a moment, he adds, "Or someone in the corridor might hear you."

Not that it's likely, but it's still possible. Snape's robes are brushing against Draco's pale skin as he stands close. He waits, considering whether Draco deserves an easy start, and decides against it, the first blow coming down hard and unforgiving against the right cheek.