A wagging tail doesn't always mean a friendly dog. It's a response to their environment, conveying their feelings about what's happening.
The tail position and wagging speed are key to understanding a dog's emotions. Tail positions are like words, while the wagging speed is the volume of their voice.
When a dog is happy or friendly, their tail is usually in a neutral or slightly upward position, wagging at a moderate speed.
A curious dog often holds their tail straight out behind them, usually without wagging. They may also stand alert with perked ears and visible forehead wrinkles.
Submissive dogs often lower their tail or tuck it between their legs. If the tail is tucked and wagging in a tight, fast motion, the dog is likely experiencing fear.
An aggressive dog will move their tail into a vertical position, often arching over their back. The tail will be very stiff and may or may not be moving.
Dogs conveying positive emotions tend to wag their tail slightly to the right, while those conveying negative emotions wag slightly to the left.