The hog is unclean. Swine actually have running sores under their hooves. Prove this to yourself. Visit a farm where swine are raised, lift up the front hoof of a hog, and apply a little pressure to the hog's toes. You will find greenish matter oozing out from between the toes. This is one small outlet for the various heinous, filthy poisons which that pig has taken into its body.
Quite frequently, this oozing artery becomes stopped up and the poison backs up into the hog's system.
When this befalls the pig, it will have very sore feet to the point where it can barely walk.
Greenish growths are then formed on various parts of its body. At this point the feed lot operator takes this pig to market for slaughter before this pig dies on him.
This is far more common than many may ever believe.