During the Kurukshetra war, we see Karna describe to Shalya, his charioteer, how he got the Brahmastra from his Guru Parashurama. First, Karna learnt from Drona and Kripa. When Drona would not give him the Brahmashira weapon, Karna left the gurukul and went to Parashurama to learn.

 
But there, one day, when Parashurama was resting with his head on Karna’s thigh, an insect burrowed into Karna’s thigh. Karna silently bore the pain so that the Guru would not be disturbed. However, Parashurama did wake up and he knew at once that Karna was not a brahmana as he had claimed but a kshatriya.

When Karna recounts this story to Shalya, he says that it was Indra who took the form of an insect to disrupt his learning. But what actually happened? Who was the insect?

We hear the truth from Narada. The Muni says that it was a worm-like creature with 8 feet and sharp teeth. When Parashurama looked at it, it died and a Rakshasa appeared in its place. This rakshasa was named Dansa or Praggrista and he had been cursed by Brighu muni for desiring his wife. The Muni had said that when Parashurama looked at him he would die and regain his form.

Having regained his form, Dansa bowed to Parashurama and then went away, finally released from the curse.