Possible Clues:

• Doesn't blab secrets, cautious
• Tactful and trustworthy
• Unobtrusive; careful and prudent
• Careful to avoid embarrassment
• Showing prudence and circumspection
• Careful one knows this answer but isn't telling everybody
• Careful touching film on DVD, say
• Tactful, separate, we hear
• Soldiers trapped in circular object alien guarded
• Modest record with Queen support backing