| enigma(noun, trouble, show, difficulty, challenge) |
| riddle(noun, trouble, show, difficulty, challenge) |
| mystery(noun, trouble, show, difficulty, challenge) |
| puzzle(noun, trouble, show, difficulty, challenge) |
| brain-teaser(noun, trouble, show, difficulty, informal) |
| problem(noun, trouble, show, difficulty, challenge) |
| closed book(noun, expression, idiom, trouble, show) |
| poser(noun, trouble, show, difficulty, informal) |
| secret(noun, trouble, show, difficulty, challenge) |
| puzzlement(noun, trouble, show, difficulty, challenge) |
| mystification(noun, trouble, show, difficulty, challenge) |
| dilemma(noun, trouble, show, difficulty, challenge) |
| teaser(noun, trouble, show, difficulty, challenge) |
| brainteaser(noun, difficulty, challenge, question, secret) |
| mystery story(noun, expression, story, mystery, narration) |
| puzzler(noun, trouble, show, difficulty, challenge) |
| difficult choice(noun, expression, trouble, show, difficulty) |
| difficult decision(noun, expression, trouble, show, difficulty) |
| difficult problem(noun, expression, trouble, show, difficulty) |
| difficult question(expression, difficulty, question, problem) |