What metaphors are used in The Thirty-Nine Steps by John Buchan?

Buchan demonstrates a true mastery of metaphorical language when it comes to delineating character. Previously, the narrator had expressed the view that a certain plump little man seemed benevolent. Later, he actually wonders in narration where the benevolence could possibly have been when the man shows his true character:

"He was sheer brain, icy, cool, calculating, as ruthless as a steam hammer...His jaw was like chilled steel, and his eyes had the inhuman luminosity of a bird’s."