Question: Wouldn't Burt and his wife get in trouble for having all the weapons in their house? Even in later movies, there is no sign they got in trouble and Burt continued to have all these big weapons on hand.
Chosen answer: No, there's nothing illegal about any of the weapons they owned. Some of them may have required a Class 3 firearms license, but even this is not difficult (just expensive) for a law-abiding citizen to obtain.
Answer: In some parts of the US, especially in far-out desert towns, home arsenals like this are the norm. There is really no limit on how many firearms or ammo American's can own. Machine guns are illegal, but can be permitted. If you have any semi-auto firearm, it's not hard to convert to a machine gun. Albeit, the firearm will fail apart fairly quickly from the abuse.
Question: When Val and Earl first come into Perfection the sign says population 14. If you add up all the characters in the movie excluding Rhonda, there's 14 people. The question is who is taking care of Melvin?
Answer: According to one of the writers, his parents were both immature ne'er-do-wells who would often abandon him for long stretches of time. So he's pretty much on his own. Hence, his parents are not counted on the population sign, since they're barely there for him. It's also mentioned in the original script (which can be found online) that they spend a lot of their time in Las Vegas, presumably gambling. (Val says the line "Why don't his parents ever take him to Vegas with them?" in regards to Melvin in scene 13).
Answer: His Uncle Nestor.
To my knowledge, nothing in the film indicates Nestor is related to Melvin.
When Nester dies, Melvin lets the audience know that was his dad.
Um... no. No he doesn't. All he does when Nester dies is shout "No way, man! You guys have gotta do something!" to Val and Earl. He definitely never says Nester was his dad. As I said above, the writers have specifically said his parents were immature ne'er-do-wells who just aren't around most of the time. In fact, it's even mentioned in the original script that his parents were often away in Las Vegas rather than taking care of him.
Question: Why does Melvin, who looks about 15, live out there alone, in a shack, with no adult supervision?
Answer: In the original script Melvin has parents, but they constantly abandon him when they make trips into Las Vegas. This was reaffirmed by the directors.
Answer: It is never stated that Melvin lives in the shack. He just climbed onto the shack's roof because it was the nearest structure. In fact, earlier in the movie when Val and Earl are pumping the septic tank, Melvin is sitting on the porch of the house. Earl even says to Melvin, "Why don't you give us a hand? most of this **** is yours."
Chosen answer: The machine is a vibrating case cleaner, which is used to polish the brass casings of pistol and rifle ammo. The "dirt" is actually an abrasive polishing compound.
BGraz