| deal breaker(noun, expression, challenge, case, matter) |
| quantum physics(expression, characteristic, strangeness, weirdness) |
| achilles heel(noun, expression, question, mysterious, secret) |
| acrostic(noun, issue, question, task) |
| air of mystery(expression, characteristic, strangeness, weirdness) |
| awkward(noun, issue, question, task) |
| bone of contention(expression, characteristic, strangeness, weirdness) |
| charades(noun, issue, question, task) |
| closed book(noun, expression, question, mysterious, secret) |
| complex(noun, issue, question, task) |
| compose(noun, issue, question, task) |
| confidential(noun, issue, question, task) |
| crossword puzzle(expression, characteristic, strangeness, weirdness) |
| crux criticorum(expression, characteristic, strangeness, weirdness) |
| diagnus vindice nodus(expression, characteristic, strangeness, weirdness) |
| duality(noun, question, mysterious, secret, myth) |
| elder statesman(noun, expression, question, mysterious, secret) |
| enfant terrible(noun, expression, question, mysterious, secret) |
| fair question(expression, characteristic, strangeness, weirdness) |
| field of inquiry(expression, characteristic, strangeness, weirdness) |