Alecto started at her brother's yell; she jumped at the house elf's appearance; and she cringed away from Amycus when his voice came from right next to her. She didn't relax her rigid position, but she moved her hands just enough to see her brother's expression. She knew it was too much to ask for him to not be angry with her any longer, but it would certinly make her feel better if he didn't look as angry as he really was.
It was long time before she spoke - mostly out of fear and shock - but when she did, her voice was quiet, muted behind her hands, and totally unsure of herself. "I didn't mean it, honest. You were parading her around like a trophey, and then she looked at me like she owned you, like she'd won, and you swore you'd tell me first if that happened, but you didn't, and then I just snapped, and I didn't even know I had my wand in my hand, and I'm sorry, Amycus, I'm sorry." By the end of her rambling explanation, she had completely removed her hands from her face and was looking at Amycus with a broken expression on her face, and she was crying again. She needed him to believe it was accident, not because she felt any remorse (because she didn't), but because she was afraid of what he would do if he didn't believe her. He might leave her, or yell like her mother did, or claim he didn't love her anymore, or any number of things, none of which Alecto thought she could handle and still be okay. Not that she was okay now, but she would live, as she was.