Theory:

7. The warm breezes of approaching summer had sent everyone, including the gardener, into the house. I was feeling drowsy myself, wondering if I should go to the pond and have a swim with Ramu and the buffaloes, when I saw a huge black cobra gliding out of a clump of cactus. At the same time a mongoose emerged from the bushes and went straight for the cobra.

8. In a clearing beneath the banyan tree, in bright sunshine, they came face to face. The cobra knew only too well that the grey mongoose, three feet long, was a superb fighter, clever and aggressive. But the cobra, too, was a skilful and experienced fighter. He could move swiftly and strike with the speed of light; and the sacs behind his long sharp fangs were full of deadly poison. It was to be a battle of champions.

9. Hissing defiance, his forked tongue darting in and out, the cobra raised three of his six feet off the ground, and spread his broad, spectacled hood. The mongoose bushed his tail. The long hair on his spine stood up.

10. Though the combatants were unaware of my presence in the tree, they were soon made aware of the arrival of two other spectators. One was a myna, the other a jungle crow. They had seen these preparations for battle, and had settled on the cactus to watch the outcome. Had they been content only to watch, all would have been well with both of them.
Explanation:

During the summer, there was a warm breeze and heat everywhere. It made everyone stay inside the house. The boy felt so tired and sleepy, and he was thinking of visiting the pond where he could enjoy a swim with his gardener Ramu and the buffaloes, when the boy saw a large black cobra moving smoothly and coming out from a bunch of cactus. Suddenly, a mongoose also came out from under the bushes at the same time, and it went straight to the cobra.

Cobra

When the sunshine hit the ground, both the cobra and the grey mongoose encountered each other under the banyan tree. The mongoose was three feet long, and an excellent fighter. The cobra knew that the mongoose is a wise animal, and it got itself ready to attack. But the cobra is also an equally strong fighter as it could attack the mongoose at high speed. And the speed of cobra is compared with the speed of light. The cobra has a hollow behind his long sharp tooth, and it is filled with a deadly poison. And so, this makes the cobra a strong attacker against the mongoose. Thus, it was a classic battle between the two champions in the garden.

Mongoose

The cobra creates a hissing sound in defiance, and it moved the tongue quickly in and out. Then cobra rose itself from the ground and spreaded his hood to fight and attack the mongoose. Also, the mongoose showed his readiness to fight by brushing his tail and raising his fur.

The participants in the fight were not aware of our author's presence atop the tree, but two other spectators, a myna and a crow were watching carefully. They witnessed everything and were settled on the cactus to watch the result. But they were not satisfied with just watching, rather they wanted to participate in the fight.

Myna

Crow

Glossary from the paragraphs $$7$$ - $$10$$ of "The Banyan Tree":

 No. Words Meanings 1. Gliding Sliding, moving smoothly/ Move with a smooth, quiet continuous motion 2. Clump Group (of bushes or trees)/ A small group of trees or plants growing closely together 3. Emerged Came out/ Move out of or away from something and become visible 4. Clearing An open space in a forest where there are no trees 5. Sacs A part (of an animal or plant) shaped like a bag/ A hollow, flexible structure resembling a bag or pouch 6. Fangs Long sharp teeth (of a snake or wolf) 7. Defiance Rebellion/ Open resistance/ Bold disobedience 8. Dart Move quickly, suddenly/ An act of running somewhere suddenly and rapidly 9. Combatants Participants in a fight 10. Spectators Those who watch a show, games, etc. 11. Outcome Result/ The effect of an action
Reference:
National Council of Educational Research and Training (2007). The Banyan Tree (pp. 124-138). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.