Source: Bhima and the snake poison
Duryodhana was very much worried. His father being blind, the kingdom was ruled by Pandu. After his death Yudhishthira, the heir-apparent, would in course of time become king. Duryodhana thought that as his blind father was quite helpless he must, to prevent Yudhishthira’s accession to the throne, contrive a way of killing Bhima.
He made arrangements to carry out his resolve since he thought that the powers of the Pandavas would decline with the death of Bhima.
Duryodhana and his brothers planned to throw Bhima into the Ganges, imprison Arjuna and Yudhishthira, and then