Oh! Pig and hog rings explained!

I asked my boss, a gentleman farmer, and he said the rings go in a pig nose to keep them from rooting - it hurts to rub the ring in the dirt/roots and les cochons are quickly disabused of the notion that it's fun. A bull ring, now - you can "turn an angry, two-thousand pound steer into a little puppy by pulling on it."

Also, look at this: