To dream of a mouth represents expression of ideas or beliefs.
To see an open mouth represents receptivity or openness to new ideas.
To see a closed mouth represents being unreceptive. It may also represent being uninterested in expressing an idea or belief.
To dream of a mouth that is muzzled or sewn shut symbolizes repression, an the inability to express yourself or to speak freely.
To dream of an open mouth with a blue tongue symbolizes openness to expressing the truth.