Possible Clues:

• Crack in ground, by the sound of it?
• Gemstone imperfection
• Scratch or nick
• Defect, blemish
• Persian ___ (rugmaker's deliberate mistake)
• Having a thermal exhaust port lead straight to the reactor of your Death Star, e.g
• Gemologist's consideration
• Weak spot in base, some might say
• Loudly suggested rule has a shortcoming
• Fatal __