Theory:

     Mr Purcell mopped his sweating brow. “Now, about the care and feeding of your doves. I would advise...”

     “Bah!” The man swung around, and stalked abruptly from the store. Purcell sighed with sudden relief. He waddled to the window and stared out. Just outside, his peculiar customer had halted. He was holding the cage shoulder-high, staring at his purchase. Then, opening the cage, he reached inside and drew out one of the doves. He tossed it into the air. He drew out the second and tossed it after the first. They rose like windblown balls of fluff and were lost in the smoky grey of the wintry city. For an instant the liberator’s silent and lifted gaze watched after them. Then he dropped the cage. He shoved both hands deep in his trouser pockets, hunched down his head and shuffled away. The merchant’s brow was puckered with perplexity. So desperately had the man desired the doves that he had let him have them at a reduced price. And immediately he had turned them loose. “Now why,” Mr Purcell muttered, “did he do that?” He felt vaguely insulted.
Explanation:

After discovering that the man had come from the prison, Mr Purcell wiped the sweat from his eyebrows. Mr Purcell later thought that he had to advise the man for the well being of doves. So he said that he would tell him how to feed and care for the doves.

But the man, on the other hand, refused to listen to Mr Purcell's advice. He said, "Bah!" The term "Bah" meant that an expression of anger or disapproval. It suggested that the man did not like to hear anything from the storekeeper. Later the man moved slowly out from the shop with his caged birds. Mr Purcell, on the other hand, took a deep breath and felt a sense of relaxation. The reason behind the statement was Mr Purcell wished that the man should go out of his shop because he realised that the man had come from the prison and felt things strangely occurring when he stepped inside the shop.

Later, Mr Purcell strolled with his fat body near the window and peered out. When he looked at his strange customer, he noticed that he had stopped walking. The weird man peered at the pair of doves he got from the pet shop while holding the cage shoulder-high. The man then unlocked the cage and reached inside, pulling one of the doves out. He flung it up in the air. He took the second out of the cage and tossed it after the first.
 
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Liberation of dove
 
The two doves drifted in the breeze like fluffy balls when he released them from their cage. It suggested that the two birds flying through the sky resembled woollen balls. After sometimes the birds eventually faded into the wintry city's gloomy grey. The man remained still for a few moments, gazing up at the two birds in the sky. He threw the cage away when he saw the birds soaring freely in the skies. Later he put his hand inside his pocket, bowed his head, and walked away.
 
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Birds faded in the sky

On the other hand, the merchant's face furrowed in puzzlement. The merchant had agreed to sell them to him at a reduced price because the customer desired it. But on the other hand, what the man did was liberated the birds from the cage. In addition, Mr Purcell was shocked to see the man's behaviour. Mr Purcell mumbled under his breath, "did he do that?" He had no idea why he had abandoned them. Finally, Mr Purcell was offended by the stranger's behaviour. He was humiliated since he had sold the doves for a low price, yet the man had set them free.
 
Through the lesson "I Want Something in a Cage", the narrator tends to tell his readers that the man had lost his ten years in prison without freedom. While he saw the caged birds in the shop, he felt himself in place of them. He had only five dollars, so he bought a pair of doves and let them fly happily in the sky. Here the man's freedom has been compared to the bird's freedom. But the storekeeper was unaware that the pets in his shop were screaming and screeching for freedom. He thought of himself as a professional and held the pets freedom inside the gilded cage. Also, the storekeeper was only concerned about the profit he would earn after selling the pets. The strange act of the customer made him feel insulted. It implies that the man had worked hard in prison, and he spent the earned amount for buying birds and letting them free. But on the other hand, the storekeeper only desired to make a profit. Finally, the storekeeper realised his insignificance and felt vaguely insulted.
 
Meanings of the difficult words:
 
S.No 
Words 
Meanings 
1 
MopTo use a cloth to remove sweat from the face
2
SweatThe clear, salty liquid that you pass through your skin
3
Pucker To tighten skin or cloth until small folds appear or of skin or cloth to form small folds
4
PerplexTo confuse and worry someone slightly by being difficult to understand or solve
5
Waddle Usually of a person or animal with short legs and a fat body to walk with short steps, moving the body from one side to the other
Reference:
National Council of Educational Research and Training (2007). Supplementary. I Want Something in a Cage - L E Greeve (36-42). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.