The story alludes throughout to the insanity of the general.
“But there was one small trait of the general's that made Rainsford uncomfortable. Whenever he looked up from his plate he found the general studying him, appraising him narrowly."
Also, the hunt is suggested early on.
"Oh," said the general, "it supplies me with the most exciting hunting in the world. No other hunting compares with it for an instant. Every day I hunt, and I never grow bored now, for I have a quarry with which I can match my wits."
"You'll find this game worth playing," the general said enthusiastically." Your brain against mine. Your woodcraft against mine. Your strength and stamina against mine. Outdoor chess! And the stake is not without value, eh?"
This is foreshadowing. The General is studying him which usually means that he is trying to look at his qualities on him and the fact that it made Rainsford uncomfortable tells that the General was studying him with a harmful intention. It did turn out to be a harmful intention because the General was trying to hunt Rainsford at the end. This was a tense point of uneasiness for Rainsford. I can just imagine how it would feel like to be studied by someone. I would probably feel very defensive.
The passages show that the general kills humans for fun, and as a sport. He thinks it is fine to do that because they are inferior to him. This hints at the fact that the general might hunt Rainsford next, for fun