A quivering tail (sometimes referred to as “mock spraying” since that’s exactly what it looks like) is usually a sign of positive excitement. In my experience, I’ve noticed the “mock spray” directed either at or near a person the cat is fond of. I can only guess that this signifies ownership with a posture that walks the tightrope between confident (body scent marking, rubbing, etc.) and unconfident (urine marking) cat language. Either way, I’ve learned to take it as a pretty high compliment!
