What is tail flagging?

Tail flagging is a behaviour exhibited by some animals, particularly dogs and cats, in which they rapidly wag their tails from side to side. It is often associated with excitement, joy, or anticipation, but can also be a sign of nervousness or anxiety. In dogs, tail flagging is often accompanied by other body language cues such as a wagging tail, pricked ears, and a relaxed posture. In cats, tail flagging can be a sign of contentment or relaxation, but it can also be a warning signal to other cats to stay away.