It would be great if dogs could speak -- in a human language, that is. They already do communicate with their noises and body language. We can tell what food they like, who their favorite person is or which cat they would love to chase. An important sign to discern from your dog's actions is aggression. You can protect yourself and your dog by reading the language that illustrates when your dog is threatened and about to pounce. The American Society for the Prevention of Cruelty to Animals advises dog parents to take the entire body language into consideration when reading the dog, breaking it down into components to make it easier to understand.
Pay attention to your dog's voice. Your dog is no doubt very vocal, and produces a wide range of sounds from whimpers and low, rolling growls to all-out barks. Whimpers can mean the dog is scared, ill or anxious. Some dogs whimper when they are very excited, or raise the volume or pitch of their bark to indicate emotion. A dog's bark is not necessarily an aggressive signal; they bark from excitement, happiness, boredom or frustration, too. A growling dog is more likely to indicate an aggressive dog -- unless he's a puppy and exhibiting a play growl.
Watch your dog's mouth. A curled upper lip which exposes his fearsome-looking teeth is generally a sign of a very agitated dog ready to snap or bite. Bared teeth are usually accompanied by a low growl. A happy dog is relaxed and his mouth is closed or slightly open, or he may be panting. A dog who is anxious may also pant. Some dogs actually do grin, especially when they are acting submissive, according to dog behavioral expert David Taylor.
Check the dog's eyes. A happy dog's eyes are of normal size and are bright. When surprised or quizzical, a dog may raise his eyelids and exaggerate his expression with a tilted head. Fear aggression in dogs is often expressed with wild-looking eyes: skin drawn back, whites of eyes exposed and pupils dilated. Dominant aggression causes the dog to fix his eyes on a person or animal, daring eye contact. If your dog's eyes look somewhat smaller than normal, he may be scared, stressed or sick, according to the ASPCA.
Note the position of the dog's tail. If he's happy, he will usually be wagging it. But a wagging tail does not always mean he's in a good mood; it can also signal aggression, which is why it should be read in context with other body signals.
If the dog's tail is between his legs, he is scared or being submissive. A dog who exhibits fearful aggression will hold his tail rigid, but down; the tail in a dominant aggressive dog is held high. This signal, along with a taut body, pricked ears and bared teeth, is warning you that an attack is imminent unless the dog is taken out of the situation.
Examine your dog's ears. A comfortable dog will hold his ears normally. When he's listening or otherwise alert, the ears sit higher on the head. If the dog's ears are pulled back slightly, he is in a friendly mood. Submissive or fearful dogs hold their ears out to the side or flattened to the head.
Watch your dog's overall posture. If he wants to play, he may bow, dipping his front legs into a crouch. If he's happy, his muscles are loose and relaxed; if he's scared, he may hunch his back in an effort to look small or may cower low to the ground. A dominant or otherwise alert dog tenses his muscles and stands erect or lunges forward. A submissive dog may roll over on his back with one hind leg raised.