| problem(noun, challenge, question, puzzle, conundrum) |
| brainteaser(noun, challenge, question, puzzle, example) |
| bugaboo(noun, challenge, question, puzzle, example) |
| challenge(noun, puzzle, conundrum) |
| cliff-hanger(noun, challenge, question, puzzle, example) |
| grabber(noun, challenge, question, puzzle, example) |
| illustration(noun, challenge, question, puzzle, example) |
| intricacy(noun, challenge, question, puzzle, example) |
| mind-boggler(noun, challenge, question, puzzle, example) |
| mystery(noun, challenge, question, puzzle, conundrum) |
| poser(noun, challenge, question, puzzle, example) |
| puzzle(noun, challenge, question, mystery, conundrum) |
| puzzler(noun, challenge, question, puzzle, example) |
| query(noun, challenge, question, puzzle, example) |
| riddle(noun, challenge, question, puzzle, mystery) |
| stickler(noun, challenge, question, puzzle, mystery) |
| stumper(noun, challenge, question, puzzle, example) |
| teaser(noun, challenge, question, puzzle, example) |
| twister(noun, challenge, question, puzzle, mystery) |