After the incident with Ekalavya, Arjuna became more serious. He was found in the training ground all the time honing his almost perfect archery skills.
Duryodhana and Ashwattama both saw this and neither of them were happy. Duryodhana, who had till now believed that the five Pandavas could easily be defeated by him in cases of need, saw that Arjuna was a seriously formidable warrior. Duryodhana realized deep down that Arjuna had the capacity to beat all of them if necessary.
The actual realization that Arjuna could defeat them came when Duryodhana saw two incidents involving Arjuna and Dronacharya.....
One day when all of them had come to the training ground, their teacher had told them that on the top branch of the tree there was a wooden bird. True enough Duryodhana had seen it. He was sure all of them could see it. The test was simple...or atleast it seemed simple...All they had to do was hit the eye of the bird.
Their teacher called Yudhishtara and asked him to aim at the bird and that they had to fire only when he said so. Before firing, Dronacharya had asked Yudhishtara, what they saw. Duryodhana realized with sadness that all of them, including the Pandavas made the same mistake...All except Arjuna. When the teacher asked them what they could see, they claimed to have seen everything...the trees, the leaves, the branches...At that time Duryodhana never understood why Dronacharya was so angry with them for that...
And then in the end Arjuna came forward.
'What do you see?'
'The bird!' Arjuna replied.
'Surely you see me, or your brothers!'
Arjuna shook his head. 'I do not even see the tree or the branches...Just the bird!' he replied, his arrow poised on the string of the bow.
'Describe the bird to me!' Droncharya further insisted.
'I...I can see only its head! Not even its body!' Arjuna said.
Dronacharya smiled. 'Shoot!' he said softly.
No sooner had he spoken the words, the wooden bird fell from the tree...an arrow in its eye....
Duryodhana looked at Arjuna with almost open hatred. He knew that the dark Arjuna with his skills was going to haunt him in the years to come...
Ashwattama looked at Arjuna with anger. He realized that to his father, Arjuna would always be more special than him....no matter what...
Dronacharya smiled because he knew that Drupada did not have a chance now...The king of Panchala was as good as defeated....
The second incident was something that worried Duryodhana, even more.
That day when they had all gone for swimming for some relief from the hot afternoon sun. Happily playing in the water, they failed to see the danger lurking near them.
Their teacher had also joined them.
That was when a huge crocodile had grabbed Dronacharya and threatened to pull him away.
'HELP!' Dronacharya shouted. He was about to shout again, when Dronacharya himself free from the clutches of the monster. Shocked and surprised, Dronacharya turned and saw five arrows in the mouth of the crocodile.....Dronacharya turned to the bank and saw Arjuna there with the bow in his hand.
Dronacharya came forward with a smile, hobbling over to the bank, ignoring the pain in his thigh. 'You have saved my life! For this I will give you the knowledge of one of the most powerful weapons ever in existence....' Dronacharya said pulling the young boy towards him.
Dronacharya pulled out a dangerous weapon as it gleamed in the sunlight. Duryodhana gasped as he saw that the weapon in Dronacharya's hands was the Bramhasira. The weapon had the power to destroy the entire world.....
'This is the Brahmasira!' Droancharya said as he watched utmost wonder and respect in Arjuna's face. 'You have shown yourself worthy for using this weapon! So I grant this to you! Remember use this only against powerful enemies like the Devas or Asuras. If you use it against any humans, it would destroy the very world!' Dronacharya looked at the young boy. 'Use it well!'
Both Duryodhana and Ashwattama burned with jealously as Arjuna learnt the mantra for the weapon....
The classes were over and the boys had gone back to the palace of Hastinapur. Dronacharya was in the home when he saw Ashwattaman sulkily sitting in the corner.
'What...' Droancharya started when Ashwattaman interrupted him. 'I want to learn how to use the Brahmasira!'
Dronacharya shook his head. 'No! That knowledge is not meant for everyone! Only people who have shown to be completely in control of.....'
'YOU TAUGHT IT TO ARJUNA!' Ashwattaman yelled. 'I am your son! Teach it to me too!'
Dronacharya shook his head. 'No...'
'FATHER!' Ashwattaman said his eyes burning with anger. 'I will not be inferior to that Pandava! You have taught that boy everything that you have taught me! And now he knows more than me....This...This...'
Ashwattaman sulked and ranted for sometime. His father tried to convince him that the weapon was not meant for all. But then Dronacharya loved his son too much.
Dronacharya gave in to his parental love and taught his son the mantra to invoke the Brahmasira...
No sooner had Drona taught the mantra to Ashwattaman, Dronacharya had a sudden flash....probably a premonition from the future or probably just a gut feeling. Dronacharya saw Ashwattaman walking all alone...friendless, without the stone in his forehead (Ashwattaman was born with a stone in his forehead. The stone was meant to keep Ashwattaman free from disease or old age)...in great pain...just walking....without any goal....
Dronacharya looked around and saw himself in his own place. The vision that he had had disturbed him real bad. He looked at Ashwattaman. '..You are not meant to follow the path of virtue!' he said before he could stop himself.
Dronacharya realized at that time, that he had committed an unforgivable folly by teaching Ashwattaman the mantra. Droancharya realized that someone was going to pay a terrible price for his mistake....