The first time she spoke out of turn, she knew that she had screwed up. Her hands had been clamped over her mouth in horror before Thranduil had even turned all the way around to glower at her.
She had been trying to convince him that she was capable of leading a patrol into the woods on her own, without Legolas or one of the other guards there to babysit her. He had, of course, shot her suggestion down immediately, and none too kindly.
And she had, of course, begun to lose her temper. She was far from incompetent, and had yet to come back from patrol unsuccessful. However, her arguments had fallen on deaf ears. He had calmly talked around her reasoning, until he finally snapped out "the woods are a dangerous place, Tauriel. You would do well to keep that in mind," and had turned his back to her, dismissing her with a wave of his hand.
The words "how would you know, you never leave the palace!" had been out of her mouth before she even had time to think about who exactly she was talking to.
Now she stood, her instincts telling her to flee while she still had all her limbs attached, with Thranduil's icy glare pinning her to the floor.
She thought for a second that he would strike her, or shout at her, but the King just stood there, his eyes seeming to pick her apart as she trembled before him.
After a long moment he straightened, turning to the door.
"Guards," he called, and Tauriel closed her eyes as the gold-plated elves stepped into the room.
"Please escort Lady Tauriel to the dungeons. She is to be locked up overnight."
He waited, watching as the guards grabbed onto her arms and began to lead her away. "Perhaps that will teach her to hold her insolent tongue."
Legolas had come to visit her that night, treating her to a stern look and a long-suffering sigh, but had stayed by her side until the morning guard brought the key to release her.