The cat lets out long heart-rending meows. If I go downstairs this means I will find her sitting in the middle of the floor outside the basement steps, looking at the floor, not me.
It means she has pooped in her litter box, and it must be cleaned immediately. Sometimes she will watch from the top step to make sure I do it right, sometimes she will wait until I am done to inspect. And then she stalks off without even a thanks.