The story of Jaratkaru who married Jaratkaru and then Jaratkaru left Jaratkaru because Jaratkaru disrespected Jaratkaru!!
Ok coming straight to the story of Jaratkaru, there are multiple versions to this story but I will narrate the one found in the Mahabharata. So a sage named Jaratkaru once saw an old man tied upside down full of mucus eaten by rat. When he tried to rescue him, he told Jaratakaru that his condition is because of Jaratakaru who has not married till now due to which his ancestors are going through hell and are eyeing the end of their lineage. Jaratkaru had pity on his ancestors and decided to marry. But he put some conditions- the girl should have the same name as him, she should never displease him, and he will not support her financially.
After a lot of search, the serpent king Vasuki decided to marry his sister Jaratkaru (also known as Manasa) to the sage Jaratkaru and accepted all his conditions. The reason for this decision was a premonition that the son born out of this union will play a vital role in the Yagya of Janmejaya and in protecting the lineage of the serpents.
So Jaratkaru was married to Jaratkaru and soon she was impregnated. One day when sage Jaratkaru was sleeping on the lap of his wife, the sun started setting. The wife thought that her husband will miss the evening prayers but she also didn't wanted to wake her up. Eventually she decided to better wake him. She wake him up to do his evening prayers. Jaratakaru became extremely angry and said do you think that the sun can set without my permission!! And at that moment he decided to leave her.
The wife Jaratkaru eventually had a child alone which was named Astika. Later, King Parikshit (son of Abhimanyu) was bitten by a snake (because of the curse that Arjuna had got when he burned down the Khandav forest to create the city of Indraprastha which k*lled the whole family of Takshak Naga who lives with Indradev). Also Parikshit was cursed by the son of a sage to be bitten by a snake when he arrogantly put a d*ad snake on the neck of the sage!! After Parikshit passed away his son Janmejaya decided to k*ll all the snakes by having a grand Yagya.
As the Yagya started the snakes begin to fall into the sacrificial fire. Takshak was afraid about the lineage of Nagas and consulted Vasuki. Vasuki sent Astika to stop the sacrifice and this was the starting point of the Mahabharata story as Astika made Janmejaya remember the great lineage he belongs to and the reason Parikshit had to d*e because of the snake bite. And then he recounted the story of the Mahabharata to the people present there which was heard by the sages and then recounted to the other sages and therefore the Mahabharata was narrated to us.
The delighted snakes offered Astika a boon in return for saving their lives. Astika said, “Let the brahmanas, who recite my account in the morning and evening, have nothing to fear from you”.
The snakes acceded to his request and said, “He who recites the following need not have any fear from us:
‘I call to mind the famous Astika born of Jaratkaru, that Astika who saved the snakes from the snake-sacrifice. Therefore it behoves you not to bite me. O snakes of virulent poison, remember the words of Astika after the snake sacrifice of Janamejaya. You shall be blessed‘.
That snake who does not cease from biting even after hearing such mention of Astika, shall have his hood divided a hundredfold like the fruit of Sinsa tree”.
This verse is called Astika Sarpa Raksha mantra and is used to escape snake bite.
यो जरत्कारुणा जातो जरत्कारी महायशाः ।
आस्तीकः सर्पसत्रे वः पन्नगान् योऽभ्यरक्षत ।
तं स्मरन्तं महाभागा न मां हिंसितुमर्हथ ।।