At least, so Amy declared afterwards.

The car, which fortunately had decreased its speed to negotiate an abrupt turn in the road, suddenly shot down a slope at the left, turned around once and stopped with a disconcerting abruptness, its radiator against a four-inch birch tree.
Clint and Amy picked themselves from the bottom of the tonneau and stared, more surprised than frightened.

Behind them, on the level road, a wheel--present investigation showed that it was the forward left one--was proceeding firmly, independently on its way! As they looked, open-mouthed, it began to wobble, as though doubtful of the propriety of going off on its own hook like that, and finally, after turning around several times, like a dog making its bed, it subsided in the dust.
The driver of the car, still clutching the steering-wheel, turned a mildly surprised gaze on the boys.

"Now, what," he asked slowly, "do you think of that ?" They both thought it decidedly strange, but they didn't say so.

Clint laughed uncertainly and took a long breath and Amy viewed his surroundings interestedly.
"When," asked Amy, "does the next car go, please ?" That flippant remark broke the tension and the driver climbed gingerly out and viewed the bare hub.