Hidden below the cheery, sunny surface of American suburbia is the seething disease of domestic violence. All too often a warm family gathering can erupt in a sudden flashpoint of aggression — brother against brother — here caught in the act on videotape. Incidentally, I couldn’t find how to mosaic out the faces, so just pretend you don’t recognize anybody. (QuickTime video. 50 seconds. 3½ MBs.)