Meaning of Mouth & swollen Snout of Dog foaming at the mouth

Relaxed and halfway open mouth, tongue slightly visible: This is equal to a smile among humans.
Yawn: For a dog it shows stress or tension. The dog is tense or restless.
Mouth closed: Attention.
Licking its lips: Worried or troubled.
Mouth closed, raised lips showing its teeth: First sign of a threat.
Mouth semi-open, raised lips showing incisors, puckered snout: Second sign of threat. If the dog is provoked, it will attack.
Mouth semi-open, raised lips showing incisors and gums, puckered snout and foaming at the mouth: Right before an immediate attack. If you ever confront a dog in this manner, never run. The dog is so tense that it will detect the slightest movement and attack. Its best lo lower your eyes, open your mouth a bit and back off slowly, without turning your back to it
dog swollen snout.