In OS X, you can't open a file when it's in the trash, right? If you try, you'll get a message like this, "The document 'xyx' can't be opened because it's in the Trash."
Today, however, I discovered that you can indeed open a file in the trash. All you have to do is have a shortcut to the file in the right hand side of the dock - where you find shortcuts to files and folders (as opposed to the left hand side, where you'll find shortcuts to applications). Such a shortcut will continue to open a document, with no warning message, even after the document has been put in the trash.
I'm pretty sure this a bug and not a feature. At some point a client of mine dragged a file that had such a shortcut to the trash. They kept using the shortcut to open the file, and didn't empty the trash for months. Then they emptied the trash. And because TimeMachine doesn't back up the trash, they were out of luck. No file to recover.