What caused Rainsford to believe Zaroff knew he was hiding in the Tree? Do you think he was right? Give reasons.

Zaroff, on his knees, studies the ground, shaking his head as though puzzled; then, he straightens up and lights a cigarette. 

[HIs] eyes...were traveling inch by inch up the tree....But the sharp eyes of the hunter stopped before they reached the limb where Rainsford lay; a smile spread over his brown face.  Very deliberately he blew a smoke ring into the air; then he turned...and walked carelessly away...

The casual way in which Zaroff acts suggests that he controls "the game."  He knows Rainsford is hiding in the tree because he sends fragrant smoke upward and stops his eyes short; then he "carelessly" backtracks along the trail he has come. From Zaroff's careless behavior stopping his search and smoking, Rainsford realizes that the general plans on prolonging the game. The use of the word hunter, suggests that Zaroff is still the predator and Rainsford is "an animal at bay," who is  unwilling to risk jumping on him since Zaroff has his pistol in hand.  Rainsford understands the control of the "game" that is Zaroff's  "His first thought made him sick and numb" after descending. The general could easily have killed him in the tree; instead, he merely sends up smoke rings to let Rainsford know that he has been given another day, just for the fun of the hunt--Zaroff is like the fisherman who tosses his catch back for another day.