So, Liel has started doing this "zero-to-shrieking" thing. It's really annoying (and painful on the ears). One moment she and her brother are playing, more or less happily. The next? He's displeased her in some way (usually deserved- he grabbed a toy out of her hand, for example), and she's making sounds usually associated with a boiling tea kettle. Or dog whistles.
If we ignore it (yeah, we're working on more hands off parenting. no, it's not lazy at all, why do you ask?), one of two things happens. Usually Zion makes a teeny attempt to pacify her, and usually that works. She instantly returns to her sunny, smiling self. Sometimes, however, if Zion is annoyed himself, or tired, or sick, he continues on his destructive course, and Liel continues on hers. At this point Robert or I feel obliged to stop knitting/reading/eating/drinking/talking, put on our Stern Parent Voice and demand that they explain what's been going on. After this, the cycle is free to repeat itself.
Parenting small children can really give one an appreciation for a cyclical view of history.