There was a snake-like man named Takshaka. Agni begged Arjuna and Krishna to destroy the forest, Khandava, where Takshaka happened to live. They listened to his request and destroyed whoever and whatever was living in the forest.
Takshaka and his wife were killed, but their son Ashwasen, who was just a little baby at the time, escaped. Indra, who was guarding the forest when Krishna and Arjuna began their destruction, created a great gust of wind which compelled Arjuna to swoon for a few seconds. In this brief time, Indra helped Ashwasen to escape.
Ashwasen grew into a mature boy. In the battle, when Karna, the great hero of the Kauravas, was fighting against Arjuna, Ashwasen entered into Karna’s arrow in the form of a snake. Karna, however, was not aware of this. Even as the arrow was being aimed at Arjuna, Krishna could see that it was a most dangerous arrow. When Karna shot the arrow, Krishna pressed Arjuna’s chariot one foot down into the earth. The arrow pierced Arjuna’s golden crown, totally destroying it, but Arjuna was quite safe.
Ashwasen, the snake, came to Karna and said, “It was I who entered into your arrow to kill Arjuna. Now please use me once again.”
“It is beneath my dignity to use the same kind of arrow twice for Arjuna,” said Karna. “I will not use it.”
“If you don’t want to use my help inside your arrow, then let me go and kill Arjuna myself,” pleaded Ashwasen. So Ashwasen went and tried to kill Arjuna, but he was killed by Arjuna instead; for Arjuna was an infinitely superior archer.
This is what Krishna, the Knower of everything, the Knower of all, can do. Had Krishna not been in Arjuna’s chariot, Arjuna’s head would have been cut to pieces by Karna’s arrow. So the Lord will always take care of His dear ones.