"Since I was born," Elsa says, shrugging, her smile wry. "My poor parents hardly knew what to do with it." She hates to think of it, really; it's just one more thing to make her feel how much of a burden she must have been to them, how difficult she made their lives. But when she was young, it hadn't been such a problem. There was fun mixed with the caution. "We never knew what caused it."

She's made her peace with that, though. It is what it is, and there's no use in wondering about the cause.