A/n: Little spoiler.
Snakes.
They are horrible beings. Sure, some don't do anything to others, but still.
Whenever Sakura and Naruto came across a snake, without any hesitation, they whip out a kunai and kill it.
Snakes bring out unpleasant memories. And the thought makes them sad.
To Naruto, snakes were evil little things. Well sometimes they were big. And when they swallowed him. And when snake-like guys corrupt his teammate and make them go insane. He hates snakes more than anything. If only that giant snake hadn't appeared.
To Sakura, snakes were poisonous creatures, one bite and you'll succumb to its poison. It makes you cold and numb. It slowly eats at you, the pain growing and growing until you cannot tame it. She has seen this before back then, and she hated it. She couldn't do anything. If only she was stronger.
Snakes.
The thing that took Sasuke away. Their teammate, friend, brother. Just when he was finally swaying from his path and Orochimaru shows up and stirs up his emotions. They would never forgive that snake.
So when they hear that Sasuke has killed the snake, they secretly smile. And the emotions come back again.