Related Clues:
- Puzzling question - sieve
- Problem - model
- Model - problem
- Ingenious puzzle - sieve
- Brainteaser - sieve
- Question - a sitter
- Sphinx's conundrum?
- Mysterious puzzle
- Something baffling
- Conundrum - model?
- WWII cipher
- Someone behaving so as to be noticed
- Riddle — German coding machine
- Coarse sieve
- Problem to be solved