"When we saw that, the Nuer asked themselves, 'Why is this happening?' Then the Nuer organized themselves to go and attack. All the people from the area joined the fight," he says.
The August attack by the Murle followed similar attacks in 2010 and 2009, with each side blaming the other, each planning revenge.
As Nashir speaks, another young Nuer limps by on crutches, an ugly bullet wound in his foot.
At the opposite end of the hospital, the ward is crowded with victims. Nyarath Kolitok, who was shot in the arm and lost her 25-year-old daughter in one of the December attacks, takes the orphaned boys whom staff members have named Peter and Paul under her care, feeding them and chattering to them. She hopes someone in Jonglei will claim them as family.
Nearby, a woman shakes her head feverishly, whimpering, eyes shut. Her toddler wanders nearby, squalling.
A boy, about 6, lies motionless as his mother, Agot Korok, spoon-feeds him. When the attack happened, her husband grabbed the boy, Anyibee, and ran.
"They came early in the morning in a big column. They started to shoot people. They shot and killed my husband and they took my daughter."
The bullet that killed her husband shattered her son's leg.
Tirito Kudumoch, 25, a Murle shot in the chest during the December attack, says his people couldn't defend themselves against the huge Nuer column.
"They had big guns like RPGs and AK-47s. In our culture, when you're attacked, you have a right to fight to protect your things from being taken. But we were disarmed … and we were sitting without guns.
"The government promised they would protect us and protect our property."
Both sides have long memories, know each other's weak points and attack at moments of vulnerability, burning down clinics, leaving no one to treat the wounded.
When Nashir was a baby, his father was shot by Murle invaders, and, with no hospitals, died a week later. He grew up with his mother's story of the killing and of the desperate attempts to save his father with traditional medicine.
As a boy, he was haunted by the idea of an enemy forever on his horizon. As soon as he was old enough, in his teens, he got a gun and joined the fight.
"I was never happy. I was angry," he says. "My mother used to tell me I should always step forward to defend my brother and sisters. Now, I and my friends take guns, and we get our revenge."