Theory:

     “My dear man, if you want them that badly, you can certainly have them for five dollars.”

     “I’ll take them.” He laid his five dollars on the counter. Mr Purcell tottered on tiptoe, unhooked the cage, and handed it to his customer. The man cocked his head to one side, listening to the constant chittering, the rushing scurry of the shop. “That noise,” he blurted. “Doesn’t it get you?”

     “Noise? What noise?” Mr Purcell looked surprised. He could hear nothing unusual.

     The customer glared. “I mean all this caged stuff. Drives you crazy, doesn’t it?”

     Mr Purcell drew back. Either the man was insane, or drunk. He said hastily, “Yes, yes. Certainly, I guess so.”
Explanation:

After making the quick mental calculation, the storekeeper told the man that he could have them for five dollars if he wanted the pair of doves. The reason behind the statement was that the storekeeper would most likely make a substantial profit despite the fifty-cent reduction. As a result, he informed the man that he would sell them for the price he requested. Then, the man agreed to purchase the fine pair of doves for five dollars.

Later the storekeeper stood on tiptoe to unhook the suspended cage. He stood on tiptoe because he was a short man who couldn’t easily take the hanging cage. The storekeeper then handed the cage to the man. Meanwhile, the man turned his head slightly, listening to the constant chattering and scurrying of the pet from the shop. At last, the man asked the shopkeeper, “That noise”, “Doesn’t it get you?” The statement implies that the man was asking about the noise coming from the shop.

After listening to the man’s question, the storekeeper asked him surprisingly about what noise he was talking about. He didn’t hear anything out of the ordinary. The reason for his statement was that he would sit in the shop every day and do his work, but he never noticed the noises emanating from his pet shop. He was blissfully unaware of it. He was just delighted because his customers would come and joyfully adore the creatures, which they would then buy at a fair price. All he cared about was making a good profit. As a result, he ignored the screeching of the animals.

After hearing the answer from the storekeeper, the man stared fiercely. The man asked, “I mean all this caged stuff. Drives you crazy, doesn’t it?” It implies that the man asked Mr Purcell whether the animals in the cage and their movements did not make him crazy, nor did they irritate him. The man said it because while he entered the shop, the activities or screeching of the caged stuff made him crazy. So he asked Mr Purcell whether the noise didn’t drive him crazy.

Later, the man’s conversation led Mr Purcell to think that the customer was insane or drunk. The basis for his assertion was that he had been running the shop for a long time, but he had not experienced any unusual things from it, and the man had behaved much differently from the first instant. As a result, he thought the man was a drunkard or mad. But on the other hand, he could not tell anything bad to his customer, so he immediately said, “Yes, yes. Certainly, I guess so.”
 
Meanings of the difficult words:
 
S.No
Words
Meanings
1
TiptoeWalk quietly and carefully with one's heels raised and one's weight on the balls of the feet
2
UnhookUnfasten or detach something that is held or caught by a hook
3
CustomerA person or organisation that buys goods or services from a store or business
4
Cocked his head Moved his head quickly
5
ChitteringMake a twittering or chattering sound
6
Scurry Of a person or small animal move hurriedly with short quick steps
7
BlurtedSay something suddenly and without careful consideration
8
CrazyAnnoyed or angry
9
InsaneExtremely unreasonable, or mentally ill
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.