If you live in one the 27 cities where Amazon offers its Prime Now service, you can have tens of thousands of items delivered to your door in an hour. On a visit to Amazon's Manhattan Prime Now location, we got a peek at how it stocks its shelves, and it looks like a total mess. But there's a perfect reason it looks that way, and it's part of the reason you can get your order in an hour.

Darren Weaver contributed reporting on a previous version of this article.

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