Theory:

     “Hello Timothy!” said Grandfather and put his arm through the bars of the cage.
 
     The tiger approached the bars, and allowed Grandfather to put both hands around his head. Grandfather stroked the tiger’s forehead and tickled his ears, and, whenever he growled, smacked him across the mouth, which was his old way of keeping him quiet.
 
     He licked Grandfather’s hands and only sprang away when a leopard in the next cage snarled at him. Grandfather ‘shooed’ the leopard away, and the tiger returned to lick his hands; but every now and then the leopard would rush at the bars, and he would slink back to his corner.
 
     A number of people had gathered to watch the reunion when a keeper pushed his way through the crowd and asked Grandfather what he was doing.
 
     “I’m talking to Timothy,” said Grandfather. “Weren’t you here when I gave him to the zoo six months ago?”
 
     “I haven’t been here very long,” said the surprised keeper. “Please continue your conversation. But I have never been able to touch him myself, he is always very bad tempered.”
 
     “Why don’t you put him somewhere else?” suggested Grandfather. “That leopard keeps frightening him. I’ll go and see the Superintendent about it.”
 
     Grandfather went in search of the Superintendent of the zoo, but found that he had gone home early; and so, after wandering about the zoo for a little while, he returned to Timothy’s cage to say good-bye. It was beginning to get dark.
Explanation:
  
Grandfather was excited to see Timothy after a long gap of six months. As soon as the tiger saw him, he came near the bars and allowed himself to be stroked in the head by him. Grandfather put both his hands into the bar, without any fear and stroked the tiger's forehead and tickled his ears. This was a routine between them when Timothy was with him. He does not forget this practice even after meeting him after a long time. The tiger had grown so used to grandfather's ways and even allowed to be smacked across the face whenever he growled. This was again an old method he used, to keep him quiet. Grandfather does not have the slightest doubt or fear when he does this to the tiger.
 
tiger looking from cage_551680.jpg
Friendly tiger
 
The tiger licks grandfather's hands and welcomes him. He also seems to be happy to see him. The only factor that stops him is a ferocious leopard from the next cage, who snarled at him. Grandfather had to shoo the leopard away from him. When the leopard was no where near him, the tiger resumed licking grandfather's hands. But when he came back, he again became meek. This had to continue for a while until a number of people who were visiting the zoo gathered around to watch the reunion of the tiger and grandfather.
 
leop2020-12-21 173002.png
leopard snarling
 
The keeper of the zoo was shocked at the incidents happening around the cage and came rushing in. Upon enquiring, grandfather informs him that the tiger had been in his care six months ago. The keeper who was new to the zoo was not aware of the situation, but encourages him to continue the conversation, as he is both surprised and happy that the tiger is getting close to someone. He explains that he had tried taming him but in vain. The tiger had always been ferocious and never responded to him, in the way it had responded to grandfather.
 
Grandfather was concerned about the tiger since the leopard kept scaring him. He wanted to talk to the superintendent of the zoo regarding the change of the tiger's cage, showing that he still thinks of him as the same cub that was once in his protection. He treats him the same way a father would protect his son from danger. Since he could not find the superintendent, he plans to bid goodbye to the tiger, as it was getting late.
 
Words with difficult meaning:
  
SI.no
Words
Meaning
1
ApproachTo come near
2
TickleTo make someone laugh, by touching them softly
3
StrokeTo move one's fingers softly over something
4
GrowlTo make a deep sound, mostly out of anger
5
SmackTo hit someone
6
SlinkTo move slowly with a purpose to hide from something
7
SuperintendentA person who maintains or looks after an office or building
Reference:
National Council of Educational Research and Training (2007). A Tiger in the House - Ruskin Bond (pp. 58- 65). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.