How did Parasurama realise that Karna was not a Brahmana?

1.	How did Parasurama realise that Karna was not a Brahmana?
Answer» When Parasurama was reclining on Kama’s lap, a stinging worm burrowed into Kama’s thigh. Blood began to flow and the pain was terrible, but Karna bore it without tremor for fear that the master’s sleep should be disturbed. When Parasurama awoke and saw the blood flowing from the wound, he said : “Dear pupil, you are not a brahamana. A Kshatriya alone can remain unmoved under all bodily torments.”

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