There's a good chance this is known, at least by the older staff, but there's 104 posts with invalid filetypes from the start of the site that still exist. Most of them are deleted but could still cause potential problems in the future. You'll find bmp, rar, mpg, wmv, mp3, 1, html, pdf, and avi.
There's also 2951 posts that still use the jpeg extension instead of jpg which I can list if you want to use a script to rename them.