Theory:

     “Think I’m joking? Well, just wait. I’ll show you sometime. It’s clear you don’t know a thing about history. Haven’t been to Mahabalipuram, have you?” he said mysteriously. “Well, when our class went to Mahabalipuram, I saw a statue of his thatha’s thatha’s thatha’s thatha’s thatha’s... etcetera, etcetera... Fact is, Mahendran here is descended from that very same ancient cat. A close relative, scientifically speaking, of none other than the lion. The Pallava lion, emblem of the Pallava dynasty!” Ravi went on, walking around the bitter-berry bush, waving a twig up and down, his eyes sparkling. “This cat is a descendant of none other than the Mahabalipuram Rishi-Cat! And if I may just remind you, they worshipped cats in ancient Egypt!”

     How he loved the sound of his own voice! Meena and Mridu exchanged looks.

     “What does that have to do with anything?” Mridu demanded.

     “Huh! I’m telling you this cat is descended... from the Egyptian cat-god... no, goddess! Bastet! Ya! That’s it!”

     “So?”

     “Well, one of the descendants of that cat-goddess was a stowaway in one of the Pallava ships, and his descendant was the Mahabalipuram Rishi-Cat, whose descendant is —” Ravi flourished his twig at Mahendran “— M.P. Poonai here... whoop EEK!” he shrieked, very pleased with himself.
Explanation:
  
Since Mridu laughed, Ravi asked whether she thought he was joking. He said she did not know anything about history. He asked Mridu if she had been to Mahabalipuram mysteriously. He explained that when he went with his class, he saw a statue of a descendant of a member of the Pallava dynasty (Thatha means grandfather in Tamil). Ravi claimed that Mahendran cat was a descendant from the ancient cat. He also said that the cat was a species close to a lion's species. Thus he arrived at saying that the emblem of the Pallavas was the lion.
 
mahabalipuram cat.jpg
*This statue is in Mahabalipuram. Ravi refers to the cat in this statue. He says Mahendran is the descendant of this Rishi-cat.
  
Ravi walked around the bush, simultaneously moving up and down a small twig in his hand. His eyes were gleaming because if his discovery. Thus he proved that the cat was a member of the Pallava dynasty and the Mahabalipuram Rishi-Cat, that he had seen. He finally added the fact that Egyptians worshipped cats as Gods, in ancient times.  He was very proud of his facts, while Meena and Mridu looked at each other. Mridu asked what did the Egyptians have to do with this cat? Ravi again explained that the cat had descended actually from the Egyptian cat-goddess, named Bastet.
 
bastet.jpg
Egyptian cat-goddess, Bastet!
 
He completed his findings by saying one of the descendants of the Egyptian cat-goddess hid in a Pallava ship to travel unnoticed; and the descendant of that cat was the Mahabalipuram Rishi-Cat, whose descendant was the Mahendran cat. He called the cat "MP Poonai" and waved the twig in his hand at the cat. He screamed in delight about his theory about the cat and felt happy for himself.
 
Meanings of difficult words:
 
No.
Words
Meanings
1
descendanta person who is descended from a particular ancestor
2
stowaway

someone who hides himself in a ship or an aircraft to travel unnoticed

3
flourishedwaved, to get the attention of someone
Reference:
*Image courtesy: https://sudhagee.com/2017/01/30/stories-in-stone-arjunas-penance-or-descent-of-the-ganga/
National Council of Educational Research and Training (2007). Honeycomb. A Gift of Chappals - Vasantha Surya (pp. 18-32). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.