Possible Clues:

• Cunning lag's position mostly connected with evidence of debts
• Stealthy and damaging
• Unfairly discriminating vicar initially put out by son's cunning
• Gradually harmful
• Subtly harmful
• 2010 horror film about a comatose child trapped in a realm called The Further
• One with common sense skirts two-thirds of railway track -- potentially harmful
• Unseen but harmful
• Devious, doing time, endless debts to pay
• Cunning and treacherous