Mac: When you move a file to the trash in OS X, you can't open it unless you drag it out of the trash. That's inconvenient sometimes, but as OS X Daily reminds us, you can just use Quick Look to preview the file. When you're browsing around in your trash, tap the space bar and you'll open up the selected file with Quick Look. You won't need to move that file out of the trash just to take a peek, which is useful if you're just trying to find a single image file you accidentally dumped in there. You've been able to do this in just about every version of OS X, but it's one of those little tips that's easy to forget about if you don't do it often.
Preview Files in Trash with Quick Look for Mac [OS X Daily]