What if your server wasn't set up to deliver certain file types properly? A common occurrence with MP3 or even SWF files. Simple enough to fix:
AddType application/x-shockwave-flash swf
AddType is specifying that you are adding a MIME type. The application string is the actual parameter of the MIME you are adding, and the final little bit is the default extension for the MIME type you just added, in our example this is swf for ShockWave File.
