A dog suddenly licks its mouth frequently and swallows, which may be caused by a variety of reasons. This may be a sign that it is not feeling well, or it may be some normal behavioral response. Some possible reasons include:

Oral problems, such as oral pain, dental problems or oral inflammation .

Digestive problems, such as an upset stomach, indigestion, or food allergies.

Thirsty and may need more fluids.

Food residue or foreign objects stuck in the mouth or throat.

Emotional factors such as tension, anxiety or excitement.

A reaction to certain tastes or substances.