My sister Elizabeth lives in a condo with two other apartments. One night, one of her neighbors left their front door ajar. Deep in the wee smalls of the morning, Elizabeth was awakened by the sound of an invader in the apartment: their cat, who had escaped and found its way through Elizabeth's front door. Elizabeth has a cat of her own, who was understandably distressed, and began hissing and spitting to demonstrate his displeasure. Invader Cat somehow clawed his way up to the top of the doorway and tried to attack Elizabeth, who fought it off with a yoga mat.