Originally Posted by viggop
I think Karna was trying to pass over as a brahmin to some guru.But,Krishna takes the form of a scorion and keeps on biting him when the guru sleeps on Karna's lap.Blood gushes forth but Karna bears the severe pain so as not to wake up his guru.After the guru wakes up and asks Karna the reason for so much blood.When Karna tells him the reason,he immediately knows that Karna cannot be a brahmin because brahmins cannot withstand that much pain as they are not strong people.Only a person from Kshatriya class(royal lineage) can withstand it and curses Karna for lying.