| Answer | Crossword Clue |
|---|---|
| HUM | Run smoothly, as a machine |
| rattletrap | any machine or vehicle that does not run smoothly |
| rattletraps | RATTLETRAP, any machine or vehicle that does not run smoothly |
| OPERATE | Run, as a machine |
| PURR | Run smoothly, as an engine |
| HUM | Run smoothly, as an engine |
