Possible Clues:

• Follows from afar, maybe
• Watches someone else's mouth
• Visually interprets the spoken word
• What one who is quite unsound has to do
• Sees what someone is saying
• 'Being totally unsound, this is what one does (3,5)'
• Watches one's language?
• Understands spoken words without being able to hear them
• Spare lid (anag.)
• Pedlar is upset, sees what you're saying