Related Clues:
- Sound from a hot tub
- Cat or engine sound
- Cry of contentment
- Run smoothly, as an engine
- Hot-tub sigh
- Satisfied sigh
- Run well
- 'This is so-o-o relaxing!'
- Kitten's call
- Response during a medical checkup
- Jacuzzi sigh
- Contented sound
- Sound from an exam room
- Contented tabby sound
- Cat's 'please continue scratching behind my ears'