Theory:

    The next day he came again to quench his body in the cool waters of the forest pool. He was there for almost an hour sliding in and out of the limpid green water, or lying stretched out on the smooth yellow rocks in the shade of broad-leaved sal trees. It was while he lay thus that he noticed another boy standing a little distance away, staring at him in a rather hostile manner. The other boy was a little older than Ranji — taller, thickset, with a broad nose and thick, red lips. He had only just noticed Ranji, and when Ranji did not say anything, the other called out, “What are you doing here, Mister?”
 
    Ranji, who was prepared to be friendly, was taken aback at the hostility of the other’s tone.
 
    “I am swimming,” he replied. “Why don’t you join me?”

    “I always swim alone,” said the other. “This is my pool; I did not invite you here.”
Explanation:
 
Ranji revisited the pool the next day to relax his body in its cool water. As usual, he dived into the pool, and for almost an hour, he moved smoothly in and out of the clear green water. It implies that Ranji enjoyed diving deep into the pool and floating on the water's surface while swimming. Moreover, he swam pleasantly in the cool, clear water without any disturbance. After swimming, he came out of the pool. Later he thought of resting for a while. So he came near to the smooth yellow rocks and stretched himself out on it.

While he was resting on the rocks, the large leaves of the sal trees provided him shade. Later, Ranji noticed a boy standing a little far away from him; he was gazing at him in an unfriendly manner.

Later the narrator stated that the boy seemed a little older than Ranji. In addition, the narrator described the appearance of the other boy to his readers. The narrator stated that the boy had a well-built body, a big nose, and thick red lips. It indicates that he appeared to be a muscled youngster.

The narrator then stated that the boy had seen Ranji at that time when he arrived at the spot. Ranji remained silent after seeing the youngster, so the boy volunteered and asked him what he was doing there. On the other hand, Ranji had expected to make a new friend but was taken aback by the bitterness of the other boy. It implies that Ranji had no friends in Rajpur; while noticing the strange boy, he thought of making him a friend. But he did not do it because the boy's harsh tone had made him feel strange and unfriendly. It seemed that the boy hated Ranji for being there.

However, Ranji thought of responding to the other boy's question. So he said that he came for swimming. He further asked the boy to join him. On the other hand, the boy rudely told him that he always swim alone in the pool. In addition, the boy stated that the pool belonged to him, and Ranji had come there uninvitedly. The statement implies that the boy thought that it was his pool, and he believed that no others had the right to swim in his pool except him.
 
Meanings of the difficult words:
 
S.NoWords
Meanings
1
Quench To satisfy a need or wish
2
Hostile Showing or feeling opposition or dislike; unfriendly
Reference:
National Council of Educational Research and Training (2008). It so happened. The Fight- Ruskin Bond (pp. 45-54). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.