Hello there!
The details from the narration relate Rainsford’s impression of Zaroff are
*almost bizarre quality about the general's face 
 *his thick eyebrows and pointed military mustache were as black as the night 
 *His eyes, too, were black and very bright 
 *the face of an aristocrat
Those are descriptive details that allow us to know how is the reaction and impression of Rainsford. 
Hope this helps.