Apple has numerous "at your fingertips" options in OS X, including icon previews, coverflow and column-view previews, as well as QuickLook and Dashboard. Of these, QuickLook is one of the most useful in allowing you get a brief bit of information about an item that does not have a preview option, or a more detailed look at the contents if the item does have a preview. If for some reason the QuickLook feature stops working there are several things you can try to get it up and running again.
When you invoke QuickLook on a folder in OS X, you are shown the folder icon along with some information about the folder. While this is convenient, QuickLook does contain a hidden "X-ray" feature that allows you to preview items in the folder, similar to the option in Windows where pictures are displayed in the enclosing folder's icon.
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