Peter had a sign about unclean animals. How could God make them unclean in the first place?

My Notes:
My Notes:
List of Clean and Unclean Animals: http://www.ucgstp.org/lit/booklets/clean/animals.html

For the distinction between clean and unclean animals various origins have been suggested; though few of them seem to have fully satisfied any one but their own originators. Omitting the most ancient ones (Origen, "Contra Celsum," iv. 93; ed. Migne, xi., col. 1171; Theodoret, on Lev. ix. 1, ed. Migne, lxxx., col. 299, and others, analyzed in Vigouroux, "Dict. de la Bible," i. 615 et seq.), only the most popular ones in our own day need be mentioned. According to Grotius, on Lev. xi. 3; Spencer, "De Leg. Hebr. Rit." i. 7, 2; S. D. Michaelis, "Mosaisches Recht," iv., § 220, etc., the distinction between clean and unclean animals is based on hygiene: it is a sanitary law.
Health Reasons
In 1953 Dr. David I. Macht, one of the primary proponents of biblical scientific foresight, conducted toxicity tests on more than a hundred species of mammals, birds and fish. He reported that in every case, extracts from meat of unclean mammals, birds, and fish inhibited the growth of lupin seedlings more than those the Old Testament called clean. Macht's methodology, known as phytopharmacology, has not been widely used by other researchers and is regarded as outdated and unreliable by modern mainstream science.
A 1985 study by Nanji and French found that there was a significant correlation between cirrhosis and pork consumption. Modern day swine raising is very different from earlier times with greater exposure to toxins but reduced exposure to pests and disease.
Pathogens
Improperly cooked meats pose a health risk because of the numerous pathogenic organisms they might contain. Only in modern times have technologies improved to the point where we can be assured that meats have been sufficiently cooked to kill these pathogens. Even today in societies where these methods are unavailable parasites are a major problem.
Jane Cahill reported in Biblical Archaeological Review that the toilets of a Jewish household in Jerusalem were examined and no parasites or infectious agents were found. A similar study done regarding Egyptians systems revealed eggs from Schistosoma, Trichinella, wire worm and tapeworms, all found in pork.
Symbolism
According to others, the law was a national one, intended to separate Israel from the neighboring nations, Arabians, Canaanites, and Egyptians (Ewald, "Antiq. of Israel," pp. 144 et seq.), and partly a sanitary one (Rosenmüller, "Scholia in Vetus Testamentum"—Leviticus). According to Keil, "Handbuch der Biblischen Archäologie," pp. 492 et seq., the law is a religious one, intended to deter men from the vices and sins of which certain animals are the symbols, which view is a mere variation of the allegorical interpretation proposed by Philo ("De Concupiscentia," 5-10).
In 1966, British anthropologist Mary Douglas published the influential study Purity and Danger: An Analysis of Concepts of Pollution and Taboo. In Purity and Danger, Douglas first proposed that the kosher laws were not, as many believed, either primitive health regulations or randomly chosen as tests of Jews’ commitment to God. Instead, Douglas argued that the laws were about keeping symbolic boundaries. Prohibited foods were those which did not seem to fall neatly into any category. Her theory was that pigs were declared unclean in Leviticus because pigs' place in the natural order was ambiguous since they shared the cloven hoof of the ungulates, but did not chew cud.
No other God before me
Of these explanations the first two have been refuted by Sommer in his "Biblische Abhandlungen," i. 187-193; Keil's opinion has been opposed by Nowack, "Lehrbuch der Biblischen Archäologie," i. 117, and others. The most popular theory at the present day is perhaps that offered by the late W. Robertson Smith, in his article "Animal Worship and Animal Tribes Among the Ancient Arabs" ("Journal of Philology," 1880), according to which the unclean animals were forbidden because they were totems of the primitive clans of Israel. This theory has been accepted by Cheyne ("Isaiah," i. 99; ii. 123-124, 303) and Stade ("Gesch. Israels," i. 408), but by Dillmann is either entirely and without discussion rejected ("Genesis," p. 382), or restricted to the prehistoric times of Israel, as being a survival of the old totem-worship and totem-clan organization, resembling in historic times the case of the horse in England, which anthropologists say is not eaten because it was once sacred to Odin, and thus tabooed (Joseph Jacobs in his "Studies in Biblical Archeol." p. 89, and similarly Salomon Reinach, "Les Interdictions Alimentaires et la Loi Mosaïque," in "Rev. Etudes Juives," xli. 144)
Other uses for the animal:
The things that God created may have been used for something other than what God created them for. Point, a Buzzard was created to scavenge the land and clean the dead and rotting carcasses.
Animals such as pigs, bears, vultures and raptors can eat (and thrive) on decaying flesh. Predatory animals such as wolves, lions, leopards and cheetahs most often prey on the weakest (and at times the diseased) in animal herds.
When it comes to sea creatures, bottom dwellers such as lobsters and crabs scavenge for dead animals on the sea floor. Shellfish such as oysters, clams and mussels similarly consume decaying organic matter that sinks to the sea floor, including sewage.
A common denominator of many of the animals God designates as unclean is that they routinely eat flesh that would sicken or kill humans. When we eat such animals we partake of a food chain that includes things harmful to humans.
Dr. Russell asks, "What is so good about 'clean' meats, and what is so bad about 'unclean' meats?" He explains that "the flesh of clean animals such as beef, and fish that have scales and fins, is ideal for the health of humans-just as we would expect from the hand of a loving Creator . . . Many land animals God designed for food provide an additional benefit in that they generally eat grasses and grains that were also designed for food" (Russell, pp. 73-74).
In contrast, David Meinz summarizes the potential health risk of eating creatures the Bible classifies as unclean. "Almost all of the creatures on the unclean list are scavengers," he notes. "In many cases they don't hunt for their own food; they eat the dead and decaying matter of our environment. A catfish does that at the bottom of a pond; lobsters and shrimp do it in the ocean. A pig will eat anything. Vultures, almost by definition, are known for their scavenger habits" (Meinz, p. 225).
I believe that God said that he made everything that was created and that it was good. Gen 1.24
Sources:
http://www.jewishencyclopedia.com/view.jsp?artid=531&letter=C
http://en.wikipedia.org/wiki/Unclean_animals
http://creationwiki.org/Clean_and_unclean_animals

Does it apply to us today?
Some say yes but most look at these scriptures and say no.
Acts 10:9-19:
9-13The next day as the three travelers were approaching the town, Peter went out on the balcony to pray. It was about noon. Peter got hungry and started thinking about lunch. While lunch was being prepared, he fell into a trance. He saw the skies open up. Something that looked like a huge blanket lowered by ropes at its four corners settled on the ground. Every kind of animal and reptile and bird you could think of was on it. Then a voice came: "Go to it, Peter—kill and eat."
14Peter said, "Oh, no, Lord. I've never so much as tasted food that was not kosher."
15The voice came a second time: "If God says it's okay, it's okay."
16This happened three times, and then the blanket was pulled back up into the skies.
1 Cor: 10:25-28
25-28With that as a base to work from, common sense can take you the rest of the way. Eat anything sold at the butcher shop, for instance; you don't have to run an "idolatry test" on every item. "The earth," after all, "is God's, and everything in it." That "everything" certainly includes the leg of lamb in the butcher shop. If a nonbeliever invites you to dinner and you feel like going, go ahead and enjoy yourself; eat everything placed before you. It would be both bad manners and bad spirituality to cross-examine your host on the ethical purity of each course as it is served. On the other hand, if he goes out of his way to tell you that this or that was sacrificed to god or goddess so-and-so, you should pass. Even though you may be indifferent as to where it came from, he isn't, and you don't want to send mixed messages to him about who you are worshiping.
Romans 14:14
13-14Forget about deciding what's right for each other. Here's what you need to be concerned about: that you don't get in the way of someone else, making life more difficult than it already is. I'm convinced—Jesus convinced me!—that everything as it is in itself is holy. We, of course, by the way we treat it or talk about it, can contaminate it.
15-16If you confuse others by making a big issue over what they eat or don't eat, you're no longer a companion with them in love, are you? These, remember, are persons for whom Christ died. Would you risk sending them to hell over an item in their diet? Don't you dare let a piece of God-blessed food become an occasion of soul-poisoning!
17-18God's kingdom isn't a matter of what you put in your stomach, for goodness' sake. It's what God does with your life as he sets it right, puts it together, and completes it with joy. Your task is to single-mindedly serve Christ. Do that and you'll kill two birds with one stone: pleasing the God above you and proving your worth to the people around you.