[gemy]

But there are different qualities of growls used in different situations. Growling is one of the few forms of "verbal" communication dogs possess. Most forms of growling serve one purpose – to get someone or something to back off.
From the Irrevant Vet:

Before explaining what the various tones and pitches may mean, it's helpful to understand why dogs growl in the first place. One theory is that most creatures (including humans) instinctively associate pitch and tone to convey the message they want. A larger animal is more intimidating than a smaller one - and a lower tone is associated with a larger animal. So a growl – a low, throaty noise – makes an animal appear more menacing.

People react the same way. If you hear a deep, gravely voice, you probably assume that the speaker is more massive. In reality, he may be a 150-pound weakling. (People are often surprised when they meet disc jockeys after hearing them on the radio – they rarely match up to their voices.)

The reverse is true, by the way. A high-pitch voice is associated with a smaller frame. Among dogs, that high-pitch is usually a whine, which is sometimes paired with submissive signals.

The Bottom Line

Growling is usually meant to intimidate someone or something to leave property or valued resources (food, toys) alone, or to indicate that the dog is scared and may bite. In other words, growling is meant to repel.

A high-pitched throaty growl usually means the dog just wants to be left alone. It doesn't normally indicate that an attack is imminent – it's a warning.

A medium-pitched, growl resonating from the chest indicates the dog is prepared to do battle. If pushed, the dog may attack.

A low-pitched, "belly growl" or growl-bark indicates that the dog is about to bite.

Why a dog growls depends on the dog and the situation, but it is usually associated with aggression. There are different types of aggression. A dog may growl when he is scared (e.g. fear-aggression) or because he is asserting his status as the alpha dog (dominance aggression). On his own property, he may growl to protect his turf from encroachment (territorial aggression) or to guard some valued resource (food or toys). He may also growl or bark when chasing or cornering some small varmint as part of a predatory sequence (in which the object is not to intimidate, but to obtain food). The dogs may also growl at people who approach them or touch them when they are in pain (pain-induced aggression). Bitches may show maternal aggression, involving growling to warn off people or other dogs after delivering their puppies or if experiencing a false pregnancy.

Dogs sometimes growl during play, such as during a rousing game of tug-of-war. A growl in this playful context is not generally meant as a threat. However, if the play gets too rough and the dog is growling, it may be better to stop playing and let everyone calm down.