What does it mean when a cat flicks just the tip of her tail?

A slow flick of just the tail tip, while the rest of the body stays relaxed, is usually mild focus or interest, the kind of thing you see while a cat watches a bird through the window or considers whether to jump onto something. It is milder than a full tail lash or thumping the tail against the floor, which usually signal real irritation or overstimulation. Reading the tail alone can mislead you, though; the ears, pupils and body posture around it tell you whether that flick means curiosity or the early edge of annoyance.