Theory:

     We all missed him greatly; but in a sense we were relieved. My wife was inconsolable. She wept and fretted. For the first few days she would not eat a thing. Then she wrote a number of letters to the curator. How was Baba? Back came the replies, “Well, but fretting; he refuses food too.”
 
     After that, friends visiting Mysore were begged to make a point of going to the zoo and seeing how Baba was getting along. They reported that he was well but looked very thin and sad. All the keepers at the zoo said he was fretting. For three months I managed to restrain my wife from visiting Mysore. Then she said one day, “I must see Baba. Either you take me by car; or I will go myself by bus or train.” So I took her by car.

     Friends had conjectured that the bear would not recognise her. I had thought so too. But while she was yet some yards from his cage Baba saw her and recognised her. He howled with happiness. She ran up to him, petted him through the bars, and he stood on his head in delight.
Explanation:
 
Although the narrator missed the bear, he was actually relieved that he no longer has to be cautious or take care of a grown bear. But his wife did not have the same feelings. She cried and went without food for days, as she missed him like his own son. When she writes to the curator to check on the bear, he writes back, saying that the bear was almost in a similar position to her. He avoided food and was seemingly unhappy. The fact that the bear who had once eaten everything including barium carbonate, and engine oil, was now refusing food, gives a clear picture of the unhappiness that the change in environment had brought to him.
 
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Crying wife writes to the zoo
 
The narrator's wife missed the bear intensely that she was not satisfied by the letter sent by the curator that he was doing well. Therefore they urged and begged all their friends who were going to Mysore, on their personal work, to check on Bruno. Everyone reported the same way that he was doing good, but was fretting and not being his happy self. He had also become thin due to excessive worrying. The narrator somehow manages to console his wife and keep her from visiting the zoo. But he could not restrain her for so long. She never forgot Bruno, and therefore she insists on the narrator taking her to the zoo. She is also stubborn to the extent that she boldly tells him that, she would leave by the next train if he does not take her in the car. She does not mind struggling a bit to see her beloved Bruno. The narrator is left with little choice and therefore takes her to the zoo.
 
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Man travelling along with his wife
 
Since it had already been months, after Bruno was taken to the zoo, the narrator and his friends predicted that he might not recognize her. They probably felt that way, since Bruno was an animal, and even humans grow apart, when in the distance. But the straight opposite was witnessed in the zoo. He recognized her even from a distance and howled with happiness. He had not forgotten her at all, in spite of months passing by. The narrator's wife ran up to him and petted him through the bars. The bear was so happy that he actually stood on his head (Upside down). An emotional reunion takes place in the zoo between the old mistress and her pet.
 
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Bear reuniting with woman
 
Meaning of difficult words:
 
SI.noWordsMeaning
1
Fret Worry
2
InconsolableNot able to be comforted 
3
RelievedHappy and relaxed 
4
CautiousCareful
5
WeptCried 
6
RestrainRestrict or limit 
7
ConjecturedTo take a guess 
8
YardsA unit of length to 3 feet 
9
PettedShow love by touching 
10
HowledMake a loud sound, especially in the case of animals 
Reference:
National Council of Educational Research and Training (2006). Beehive. The Bond of Love - Kenneth Anderson (pp.113-118). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.