I think that the mud on Buffy's face--and Buffy's face only--has to do with her "dark nature." I am just speculating, so...
Double Post: -
Okay...here's what I think about Xander's dream. Throughout his life, Xander(and Willow) have always thought of themselves as geeks or people who never included in life..ie not popular, not atheletic, not belonging. The bathroom scene is a reflection of Xander's belief that people were judging him, making fun of him, talking about him, etc. He reflects as if he is part of an experiment. That people would want to study him, to judge him, to see what sets him apart from being normal. And what's a more perfection comparison than being a rat in lab cage.
The Apocalypse Now is scene is a little bit more in depth. First some background, Apocalypse Now is movie came out in 1979, starring Martin Sheen(President Bartlett in the West Wing), Marlon Brando(the Godfather), and directed by Francis Ford Coppola. It is based on the Joseph Conrad classic "Heart of Darkness," but the movie takes places during the Vietnam War.
If you have never seen it, I really recommend that you do. It is one of the best movies of all-time. The only drawback is that it is about 4 hours long. (Check out the early cameo by Harrison Ford, and the Ride of Valkyre scenes.)
It is about an Army Captain(Sheen)on the verge of depression and madness(check-out the opening scenes in the motel room) who is ordered by his Superiors to go up the Nung River in a naval patrol boat to arrest and/or kill an Army Colonel who has gone renegade. While going up the river, Sheen keeps on getting messages and reports about what could've happened to the Colonel and why he went renegade with his army of natives. Reading the files, Sheen realizes that the Colonel went AWOL because he believes that the Army is not winning the war the right way. In fact, the Colonel believes that the Army doesn't want to win at all. Disaffected, the Colonel goes AWOL and starts his own little war. The only difference is, as Sheen concludes is that he is WINNING the war!! Herein lies the Sheen's madness. He is told by his superiors that he has to stop a man who is WINNING the war. This of course, gives credence to the fact that the Army doesn't care whether or not they win or lose, and that Sheen is nothing more than an errand boy. What he has done to fight the war has no relevance because his superiors don't want to win.
Sheen makes his way down river--past a couple of firefights, a French rubber plantation, and helicopter full of Playboy Playmates that crashes in the jungle. Finally, Sheen arrives at his destination up the river and is immediately captured by Brando. Here, Brando and Sheen talk in a small dark room with Brando siluetted only by patches of light. He is a complete mystery.
After talking with Brando, Sheen finally realizes the Brando is doing what the Army won't do to win the war, and he starts to question whether or not to finish his mission. Brando just completely devestates not only Sheen's purpose as a soldier but also his believe that he has any revelence in his duties.
This could be said the same for Xander. He is not a witch. He is not a Slayer. He is not a Watcher. He is as Cordelia painfully put it--a zeppo. A tag-a-long. Not only in fighting Vampires, but in his life as well. He goes from one job to another--ice cream man, pizza delivery guy, door-to-door salesman, etc. He starts to question his life and his path in it.
Watching the movie, Giles blurts out, "oh it's all about the journey," meaning the trip up the river into the unknown. Which is what life is all about--a journey filled with the unknown. Everyone knows what they are(seemingly) with some purpose except for Xander. He excuses himself, and heads into the bathroom where he eventually finds himself as Synder's prisoner ala Apocalpyse Now. Immediately Synder begins to question him--who are you? where are you going? what is your purpose? Just as Brando was questioning Sheen's purpose, which is based on the lie that the Army wants to win. That Sheen was valuable to the Army's cause.
The same is asked of Xander in relation to the Slayer. What does Xander really do? What is his real function in regards to fighting evil? Xander believes that he is valuable...but he can't do any spells, doesn't have the strength to kill vampires, and can't read five languages. In the scene with Synder, Xander tries to bluff his way into telling Snyder that he is a comforter, or a soldier, or conquistador, like he told Joyce. But, Synder knowing the truth just lays into him. "I walked by your guidance counselor's office one time, "Synder begins," A bunch of you were sitting there ... waiting to be shepherded. I remember it smelled like dead flowers. Like decay. Then it hit me. The hope of our nation's future is a bunch of mulch. You're(Xander) a whipping boy. Raised by mongrels and set on a sacrificial stone."
Xander just stares at him, and he realizes that Synder--his arch nemisis from high school is right. He is nothing. He does nothing important. He isn't relevant. He contributes nothing not only to the Slayer, but to his life in general. I mean he is still living in his parent's basement. In fact, it isn't until the next season that Xander finally stands up for himself. He gets a new permanent job, he gets his own place. And he is able to start taking care of himself after he gets fed up as being as he says it himself, "Dammit! You know what? I'm sick of this crap. I'm sick of being the guy who eats insects and gets the funny syphilis. As of this moment, it's over. I'm finished being everybody's butt-monkey!"
