On the 10th day of the war, Bhishma falls, and Drona is named the supreme commander of the armies. He promises Duryodhana that he will capture Yudhishthira, but then he repeatedly fails to do so. Duryodhana taunts and insults him, which greatly angers Ashwatthama, causing friction between Ashwatthama and Duryodhana. Krishna knew that it was not possible to defeat an armed Drona. So, Krishna suggested to Yudhishthira and the other Pandavas, if Drona were convinced that his son was killed on the battlefield, then he’d disarm himself in grief. Krishna hatched a plan for Bhima to kill an elephant by the name Ashwatthama while claiming to Drona it was Drona’s son who was dead. Ultimately, the gambit works (though the details of it vary depending on the version of the Mahabharata), and Dhristadyumna beheads the unarmed, unaware sage.