Theory:

     Grandmother always fussed when Grandfather brought home some new bird or animal. So it was decided that Toto’s presence should be kept a secret from her until she was in a particularly good mood. Grandfather and I put him away in a little closet opening into my bedroom wall, where he was tied securely — or so we thought — to a peg fastened into the wall.
 
     A few hours later, when Grandfather and I came back to release Toto, we found that the walls, which had been covered with some ornamental paper chosen by Grandfather, now stood out as naked brick and plaster. The peg in the wall had been wrenched from its socket, and my school blazer, which had been hanging there, was in shreds. I wondered what Grandmother would say. But Grandfather didn’t worry; he seemed pleased with Toto’s performance.
Explanation:
 
If the narrator's grandfather is interested in running a private zoo, his wife is not supportive and has a particular viewpoint on raising animals or birds. Since the narrator's grandmother disapproves of her husband taking any new bird or animal into the house, he wishes to keep Toto's arrival a secret.

Grandfather had decided to let his wife know about Toto when she was in a good mood. So, the narrator helped his grandfather to keep Toto secretly in his bedroom wall closet. Since Toto would not remain in the same place, they safely tied it to the peg attached to the wall. After a few hours, when the narrator and his grandfather returned to the narrator's room to release Toto, they found many messy things happened over there.
 
Toto inside the narrator’s room.jpg
Toto inside the narrator’s room
 
Toto had damaged the entire room. It had torn the fancy wallpapers that were chosen by his grandfather. The walls looked empty without those wallpapers. The worst part is, Toto broke the hook on which the narrator's blazer was hanging and tore it too.
 
When the narrator was concerned about Toto's activities, he noticed that it had no effect on his grandfather. He appreciated Toto's work.
 
Meaning of difficult words:
 
S.No
Words
Meaning
1.
ShredSomething that has been torn
2.
BlazerA type of jacket
3.
Fastened Attached, joined or fixed
4.
MessyRefers to disorder or untidiness
5.
Ornamental Decorative
6.
WrenchTo pull something suddenly and violently
Reference:
National Council of Educational Research and Training (2006). Moments. The Adventures of Toto – Ruskin Bond (pp. 7-10). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.