Related Clues

• Mental challenge
• Knot
• Poser
• Lingerie shown during a preview?
• "If three hens lay three eggs in three days ...," e.g.
• Hard puzzle
• Riddle
• Difficult puzzle
• Puzzle
• *Tricky puzzle
• It may call for lateral thinking
• Developing a barren site may be a tricky problem
• Difficult problem
• Little mental workout