Mahabharat S04 E03 Dronacharya teaches Arjun

On seeing Arjun’s archery skills, Dronacharya gives him more lessons. Meanwhile, Duryodhan provokes Ashwatthama against Arjun. Later, he fights with Bheem for insulting Dushyasan. Bheem falls in the marsh while fighting. Arjun saves him with his bow and arrow. But how?