I found this recently on Gamespot.com under farcry easter eggs:
Far Cry Easter Eggs
If you park a buggy in an unsafe spot, such as on a flight of stairs in the Fort level, eventually a pig will get in and drive it back to the road and park it. Be careful, the pig will run you over if you get in the way.
i've tried this briefly, with no result (partly because mercs kept standing behind my buggy and blowing it up) anybody know if this is true?