User blog comment:Admiral Sugar/Thoughts on Devil Fruits/@comment-3130944-20140216101920/@comment-53539-20140217111138

There is something I once got asked; "How does a fly stop a train?".

Answer; when two forced collide with each other, there is a sudden stop, therefore if the fly bangs into the train, the train stops for a moment before continuing. However, the moment the fly causing the train to stop when the fly hits the train cannot be measured due to how quickly it occurs. There it never seems like the train has ever stopped.

Likewise, even if two people eat the fruit, only one will get the power. The person who "eats" the fruit first, by the slightest split millisecond, will get the power. Its basically like how you can't measure the fly stopping the train, you might not be able to tell who ate fruit with any measurable time, but 1 will get the power before the other because they were ahead by that unmeasurable time.