How To Interpret Your Dog's Body Language
Over the years dogs have evolved an elaborate system of body language, facial expressions, and vocalizations to communicate with each other and all of these signals are easily understood by other dogs, just as they could/should be by their human counterparts.
 

AGGRESSIVE

Ears

Forward or back, close to head.

Eyes

Narrow or staring challengingly.

Mouth/Teeth

Lips open, drawn back to expose teeth bared in a snarl. Possible jaw snapping.
Body Tense. Upright. Hackles on neck up. Completely Dominant position.
Tail Straight out from body. Fluffed up.
Vocalization Snarl. Growl. Loud bark.
 

ALERT

Ears

Perked-up. Turning to catch sounds.

Eyes

Open normally or wide.

Mouth/Teeth

Mouth closed or slightly open with teeth covered.
Body Normal. Possibly standing on tiptoe. Slightly Dominant position.
Tail Up. Possibly wagging.
Vocalization None. Low whine or alarm bark.
 

ANXIOUS

Ears

Partially back.

Eyes

Slightly narrowed.

Mouth/Teeth

Mouth closed, or slightly open in a "grin."
Body Tense. Slightly lowered in a Submissive position.
Tail Partially lowered.
Vocalization Low whine or moaning-type bark.
 

CURIOUS/EAGER/EXCITED

Ears

Perked-up, forward-pointing.

Eyes

Wide open.

Mouth/Teeth

Mouth open, teeth covered. Possible panting.
Body Normal stance. Possible wiggling, standing on tiptoe, or pacing.
Tail Up. Wagging.
Vocalization Excited short barking, whining.
 

DOMINANT

Ears

Up straight or forward.

Eyes

Wide open, staring.

Mouth/Teeth

Mouth closed or slightly open.
Body Very tall posture. Hackles may be up.
Tail Stiffened and fluffed. Up or straight out from body.
Vocalization Low, assertive growl or grunt.
 

FEARFUL

Ears

Laid back flat and low on head.

Eyes

Narrowed, averted. Possibly rolled back in head, whites showing.

Mouth/Teeth

Lips drawn back to expose teeth.
Body Tense. Crouched low in submissive position. Shivering, trembling. Possible secretion from anal scent glands.
Tail Down between legs.
Vocalization Low, worried yelp, whine, or growl.
 

FRIENDLY

Ears

Perked-up.

Eyes

Wide open. Alert look.

Mouth/Teeth

Relaxed, possibly slightly open, "smiling" mouth.
Body Normal posture. Still, or possible wiggling of whole rear end.
Tail Up or out from body. Wagging.
Vocalization Whimpering, yapping, or short, high bark.
 

PLAYFUL/HAPPY

Ears

Perked-up and forward, or relaxed.

Eyes

Wide open. Sparkly/merry-looking.

Mouth/Teeth

Mouth relaxed and slightly open, teeth covered. Excited panting.
Body Relaxed, or front end lowered, rear end up in the air, wiggling in a play-bow. Excited bouncing and jumping up and down. Circling around and running forward and back in an invitation to play.
Tail Wagging vigorously.
Vocalization Excited barking. Soft play-growling.
 

SUBORDINATE (SUBMISSIVE)

Ears

Down, flattened against head.

Eyes

Narrowed to slits or wide open, whites showing.

Mouth/Teeth

Lips pulled way back from teeth in a "grin". Nuzzling or licking other animal or person on face.
Body Lowered to ground, front paw raised. Lying on back, belly up. Possible urine leaking/dribbling. Possible emptying of anal scent glands.
Tail Down, between legs.
Vocalization None, or low, worried whining. Possible yelping/whimpering in fear.