Related Clues:

• Enter silently, as a cat burglar
• Furtively 67-Across
• Add subtly
• Arrive unnoticed
• Approach stealthily, with 'on'
• Approach stealthily, with "on"
• Prepare to surprise, with 'on'
• Enter undetected and transgress, bagging duck
• Slyly add
• Prepare to scare, with "on"
• Unobtrusively add