Giant hogs were on the OD&D wandering monster matrix. This is why.
"Before the rules for D&D were published Old Greyhawk Castle was
13 levels deep. The first level was a simple maze of rooms and corridors,
for none of the participants had ever played such a game before. The second level had two unusual items, a Nixie pool and a fountain of
snakes. The third featured a torture chamber and many small cells and
prison rooms. The forth was a level of crypts and undead. The fifth was centered around a strange font of black fire and gargoyles. The sixth
was a repeating maze with dozens of wild hogs (3 dice) in inconvenient
spots, naturally backed up by appropriate numbers of Wereboars. The seventh was centered around a circular labyrinth and a street of masses
of ogres. The eighth through tenth levels were Caves and caverns featuring
Trolls, giant insects, and a transporter nexus with an evil Wizard (with a number of tough associates) guarding it. The eleventh level
was the home of the most powerful wizard in the castle. He had Balrogs
as servants. The remainder of the level was populated by Martian
White Apes, except the sub-passage system underneath the corridors
which was full of poisonous critters with no treasure. Level twelve was
filled with Dragons. The bottom level, number thirteen, contained an
inescapable slide which took the players 'clear through to China', from
whence they had to return via 'Outdoor Adventure', It was quite possible
to journey downward to the bottom level by an insidious series of
slanting passages which began on the second level, but the likelihood
of following such a route unknowingly didn't become too great until the
seventh or eighth level. Of the dozen or so who played on a fairly
regular basis, four made the lowest level and took the trip: Rob Kuntz,
now a co-referee in the campaign went alone and three of his friends
managed to trace part of his route and blunder along the rest, so they
followed him quickly to the Land of China. Side levels included a barracks
with Orcs, Hob-goblins, and Gnolls continually warring with each
other, a museum, a huge arena, an underground lake, a Giant's home,
and a garden of fungi."
from "How To Set Up Your
Dungeons & Dragons
Gygax," europa 6-8 April 1975.
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