Question: When meditating, why does the practitioner have to close his mouth, curl his tongue, front teeth slightly touching together, with incisors against incisors?

Answer by Master Vi-Kien:

When we curl our tongue,  mouth closed, incisors against incisors, we are concentrating our three energies: seminal essence energy, vital breath energy, spiritual energy. Like the seal of the Goddess of Mercy (Guan Yin), which exists since a long time. When we clasp our hands like this, we form the Guan Ying seal, we concentrate our three energies. By curling our tongue, incisors against incisors, we will focus our energies and help them elevate higher.