Thick liquid flowing from a dog’s mouth may be caused by heatstroke, oral problems, lack of vitamin B, gastroenteritis, canine distemper, etc. If the dog has this condition in summer, the possibility of heatstroke is relatively high and needs to be Help the dog relieve heat. If the dog often suffers from this condition and is in poor spirits and has a loss of appetite, it is best to take the dog to the pet hospital for examination and treatment.