At the hospital at which she (apparently, sometimes, when she feels like it) works, Dana Scully and the horribly named Special Agent Einstein examine victims of a possible viral agent which is attacking the human immune system, causing them to fall victims to diseases they've already been vaccinated for, such as smallpox. That ugly looking, infected wound above? That's a smallpox vaccination scar. WTF? Gross. The idea behind this particular storyline is actually quite ingenious, and came from the show's longtime science adviser, Anne Simon. It's like alien HIV, and the only cure is based in extraterrestrial DNA. It's a shame the show didn't go a little more in-depth on the science side of things.