Once there lived a snake named Mandavishya nearby a mountain. He was very old due to which he was unable to get his food by preying frogs.
One day he was very hungry and there were no food near him. He began to thought, “Now I became too old to hunt for food and if I did not get any food it became very weak to me. I will not be able to live anymore without food. I have to think some solution for this problem.”
Suddenly an idea struck in his mind. According to the plan he went to the nearby pond, where a number of frogs lived. As he reached there he relaxed near the bank of the pond pretending that he has no intention to hunt. He behaved as he had nothing to do with the frogs.
After seeing him at the bank of the river the frogs started to ran away, but as the snake was not hunting, so they gathered at one place and reached the snake. One of the frogs said to him, “O snake! Why do you not hunting today, though it is your behaviour.”
Then the snake started pretending and replied, “Now I have no desire for food, as I am an unlucky person.” The frog asked the reason for this, and then the snake explained him, “Dear, last night when I was moving here and there in search of food, but I did not get any food, so I bit a Brahmin's son in frustration of not getting any food. Then the Brahmin got angry and cursed me that from now onwards I shall be not able to prey any frog else I have to serve frogs. I live my life what frogs offer me to live. Thus, I am here, to serve any frogs who want my services. I can also give a ride on my back to any frog who want to do so.”
The frogs get surprised and he reached the kings of the frogs. When the king heard this news, he approached the snake along with his ministers. The king asked him that the news was really true. On being assured by the snake that he approached no harm to him, the king decided to take a ride on the snake’s back first. As the king sat on the snake’s back, he rode the king around the pond very carefully, so the king was very entertained. All the ministers even the other frogs also ride on the snake’s back one by one and they were very delighted also.
The snake too done his job carefully and proved himself a good rider by exhibiting many styles of crawling. All the frogs and especially the king of frog were very happy. They jumped and leaped all the way of returning home.
The snake thought himself that he got succeed in his plan. So the next morning he pretended to be very weak and ill and even crawled slowly. On the other hand the king of frogs was very eager to start his morning with a ride on the snake’s back as last day. As he reached the snake he came to know about his health. He asked him about his health, the snake replied, “Sir, I am feeling well today. I am too weak to even crawl. Though I have not eaten anything for many days, so must need some food to eat to get some energy to give a ride to you.”
Then the king thought for a moment, then consulted his ministers and then decided that they must serve the snake with one frog a day to keep him healthy and strong. After heard this the snake was very happy, because that was what he had planned for. The snake praised the king of frog for his kindness and sympathy, and then gave him and other frogs a ride on his back.
From that day the snake gave ride to the frogs everyday and then got a frog to eat. In this way within few days the snake gained much strength and became very healthy. On the other hand, the number of frogs decreasing day by day and the king of frog was very disappointed on realising the frogs were decreasing in numbers and there were only a few remained.
The frog’s snake cannot understand the real motive of the snake behind all this even now.
One day a big black snake approached the bank of the pond. When he saw the excited frogs hopping and jumping in joy and riding on the snake’s back, he got very surprised. Then he asked the snake the reason. He said, “O friend! Why are you carrying frogs on your back? They are our food, then why are you doing so?
Then the old snake explained everything to the black snake. He continued, "I have enjoyed many different tastes by eating many different frogs here. I have getting this easy way of life, and enjoying it here." 
As thus time passed away, the snake had started eating even the lager snakes, the king’s ministers and the king's relatives. Finally one day he ate the king also and thus, all the frogs of the pond finished.
 
The wise indeed say:

Beware of deception from all quarters including your friends.