The Th sound
How the Th sound looks and how it is made:
The sound for words like /th/umb, is from the tip of the tongue pressing into the bottom of the front top incisors. The air is blowing out as the sound is produced, the jaw (lower mandible) is elevated, and the mouth is slightly open. The feeling with this sound is that the tip of the tongue is gently pressing into the tips of the top-front incisors while the air is blowing through.