"The pig is regarded among them as an unclean animal, so much so that if a man in passing accidentally touch a pig, he instantly hurries to the river, and plunges in with all his clothes on. Hence, too, the swineherds, notwithstanding that they are of pure Egyptian blood, are forbidden to enter into any of the temples, which are open to all other Egyptians; and further, no one will give his daughter in marriage to a swineherd, or take a wife from among them, so that the swineherds are forced to intermarry among themselves. They do not offer swine in sacrifice to any of their gods, excepting Bacchus and the Moon, whom they honour in this way at the same time, sacrificing pigs to both of them at the same full moon, and afterwards eating of the flesh. There is a reason alleged by them for their detestation of swine at all other seasons, and their use of them at this festival, with which I am well acquainted, but which I do not think it proper to mention. The following is the mode in which they sacrifice the swine to the Moon:- As soon as the victim is slain, the tip of the tail, the spleen, and the caul are put together, and having been covered with all the fat that has been found in the animal's belly, are straightway burnt. The remainder of the flesh is eaten on the same day that the sacrifice is offered, which is the day of the full moon: at any other time they would not so much as taste it. The poorer sort, who cannot afford live pigs, form pigs of dough, which they bake and offer in sacrifice.
To Bacchus, on the eve of his feast, every Egyptian sacrifices a hog before the door of his house, which is then given back to the swineherd by whom it was furnished, and by him carried away. In other respects the festival is celebrated almost exactly as Bacchic festivals are in Greece, excepting that the Egyptians have no choral dances. They also use instead of phalli another invention, consisting of images a cubit high, pulled by strings, which the women carry round to the villages. A piper goes in front, and the women follow, singing hymns in honour of Bacchus. They give a religious reason for the peculiarities of the image. "
-Herodotus, Book 2
Egyptians considered the pig an unclean animal. Hmmm...