"Beware of deception from all quarters including your friends".
There was an old snake named Mandavishya, who lived near a mountain.
Due to his old age, he was unable to prey on frogs. He thought, "I am too old to hunt for food. I will not be able to live long without food, and it is only going to make me weaker to hunt, as well. I have to think of something".
Suddenly, an idea struck him. As planned, he went to a nearby pond, which was full of frogs, and relaxed on the bank of the pond without any intention to hunt. He behaved as though he had nothing to do with the frogs.
At first the frogs ran away, but as he was not hunting, the frogs gathered some courage and approached him. One of them asked, "O Snake! Why do you not hunt, as is your behaviour?"
The snake replied casually, "I have no desire for food, as I am unfortunate. I'll explain to you. Last night, when I was wandering about in search of frogs, I bit a Brahmin's son in frustration of not finding any prey. The Brahmin cursed me. He said, 'From now onwards, you shall be able to do nothing but serve frogs. You will have to live off what frogs offer to you!' And so, I lie here, to serve any frogs who wants my services. I can give a ride on my back to any frog who wishes for a ride"
When the news reached the king of frogs, he visited the snake along with his ministers. On being assured by the snake that he means no harm, the king decided to take a ride on the snake's back. The snake rode him around the pond, and the king was very entertained. Even the ministers and other snakes took turns to ride the snake, and they were very entertained, too.
The snake, too, proved himself a good entertainer by exhibiting various styles of crawling. The frogs, especially the king of frogs, were delighted. The frogs jumped and hopped all the way.
The next morning the snake pretended to be weak and crawled slowly on purpose. The king of frogs, on the other hand, was excited to start the morning with a ride on the snake's back. He observed the snake's behaviour and enquired.
The snake replied, "I am too weak to crawl. I have not eaten for so long, and must eat something to be strong to give you a ride."
The king of frogs thought for a while, consulted his ministers, and decided that they must serve the snake one frog a day to keep him strong. This was what the snake had planned for. He praised his kindness, and gave him and the other frogs a ride on his back.
From then onwards, the snake gave ride to the frogs, and got to eat one frog every day. In a short time, he regained strength. On the other hand, the king of frogs was too excited to realize the frogs were rapidly decreasing in numbers and there were only a handful of them that remained.
The frog king was so completely taken in by the snake's talk that he did not understand his real motive.
One day, a big black snake arrived at the bank of the pond. He was very surprised to see the excited frogs hopping in joy, and riding on the snake's back.
The black snake enquired, "O friend! Why are you carrying frogs on your back? They are our food!"
The old snake explained everything to the black snake. He continued, "I have discovered many different tastes after eating many different frogs here. I have this easy way of life, and enjoying it here."
Over time, the snake had eaten even the larger snakes, and started eating the ministers and the king's relatives. Finally, one day, he ate the king also and thus, the entire frogs in the pond perished.
The wise indeed say: Beware of deception from all quarters including your friends.