The place where “Their worm dieth not,” is that place reserved for the sons of perdition, who live with Satan and his angels and for whom there is no forgiveness.
The gift of tongues is one of the prevalent manifestations of the Holy Spirit in the Mormon Church today.
Because of Satan’s rebellion against God and his avowed status as God’s enemy, Satan could never be forgiven.
Satan cannot hear the thoughts of our hearts when we pray silently. We are commanded to pray vocally as well and should not fear Satan but trust God.
Satan cannot read our thoughts, but Satan can discern our thoughts from our words and actions.