Why does the protagonist curse the dog?

The man cursed the dog because the dog showed no signs of faltering.... he is angry, but even more likely resentful.

And all the time the dog ran with him, at his heels. When he fell down a second time, it curled its tail over its forefeet and sat in front of him facing him curiously eager and intent. The warmth and security of the animal angered him, and he cursed it till it flattened down its ears appeasingly.