AN: Based on Michael Weatherly's statement "Ziva is a sociopath."

On some level, Ari had always known that there was something fundamentally wrong with Ziva.

(He could never see anything in her eyes.)

In most respects, she seemed like a normal child. Except…except, well, there was something missing. When Tali came along years later, it only confirmed his suspicions that Ziva was not normal.

Ziva was special; she was something to be admired and adored but never thought of as safe. Wild animals cannot be tamed. He remembers that she always moved like a predator, even when she crawled as a baby. When she smiled it was too much or too little or at the wrong time and never masked what lay beneath. Not to Ari, anyway. If she cried, it was because she was in physical pain. When others cried she would only watch in polite disinterest.

They had a pet rabbit as children, and their Aunt had a dog. Ziva claimed it was an accident that she had let the hound get to the little creature. But Ari remembers what happened. She opened the hatch and let the dog off the tether and sat on the windowsill to watch. And when it was dead he remembers watching from a distance as Ziva stood over what was left of it for a very long time, and he remembers wondering What are you thinking, little sister? And what do you feel, if anything at all?

When she was barely out of her teens they had the only conversation about on the subject that they would ever have. They were both still in black from their sister's funeral, sitting in the false brightness of the David house kitchen.

Ziva ran her fingers over the dining table and said, "Tali was good person. I love her." Ari had said nothing, but he did doubt. Then she had looked at him with her too-dark eyes and said: "I know what you think of me, that I am a monster. But I am only what I am, and you are an idiot if you think you're not a monster like me. We have the Family Disease." Then she had stood and was almost out of the door and into the backyard when she turned and told him fiercely "I love Tali and I love you."

Standing there in the basement, he should not have been surprised when he saw the darkness at the top of the stairs shift.

Yes, his sister loved him and he loved her. In the end, though—