That's the odd thing: I scanned the posts for instances of words appearing within other words and the like, and couldn't find any. Not in the tags, text, usernames, etc. In some cases it was just an untagged, reblogged image with no text whatsoever, posted by someone with a username unrelated to anything I'd black listed. I'd say it had something to do with the image file names, but given how often it was happening, I doubt that Tumblr just happened to generated tons of random strings of numbers and letter that just so happened to have "Supernatural", "Sherlock" and "Dr. Who" in them.