I like it. Simple, useful, sentimental, and not at all overpowering. How big an object will fit into it? If someone's hand is caught in it, will the millstone magically keep grinding and pull them in or does it require manual turning of a crank? If gold is ground up, will the resulting bread be a sparkling glitter-gold bread?
As strange as it sounds, I could see this item as a way to "destroy" an indestructible evil artifact. The artifact wouldn't be destroyed; it would just change forms to flour and thereafter baked into safe, edible, and tasty bread. "Give us the Conqueror's evil Medallion of Malice, or we will kill you and take it anyway!" "I ground it into flour to make my bread! What now, punk?"
Fun thought. I enjoy thinking of a herd of ankle-sized oxen. The picture provided makes it a little difficult to picture the oxen as blue though. I thought it was very clever to work out why the Bobeerin always die in captivity. Nicely done there. The first paragraph is very artistic with good flair, but it really doesn't flow right with the rest of the submission; it easy to read, but it lacks the flair. In general, I really like it. It could be very fun flavor text for any tundra campaign.
Often when a classroom is full of unruly students, it can become difficult for a teacher to maintain order while teaching an effective lecture. In cases like these, instructors often require each student to wear a Ring of Mutual Exclusion during the class period. This makes each student feel like he or she is the only student in a large, empty classroom. The instructor usually finds this a much easier environment to teach in. The professor will occasionally slip on a ring for a second just to see if any of the students aren't wearing theirs.
Some of the more eccentric thrill seekers will arrange for as many as a dozen gladiators to fight to the death in a small arena while each is wearing a Ring of Mutual Exclusion. Each combatant is unable to see his opponents or even feel them until, by randomly swinging his sword, he finally draws blood. An archer is usually hired to wear a ring and oversee the combat. If a contender should remove his ring, he would instantly become veiwable by the archer and subsequently shot until he died. Such tournaments often attract a large bidding competition.
Easter Egg Hunt:
During a race or scavenger hunt, the overseer will often require the competitors to wear Rings of Mutual Exclusion to provide a little more viewing pleasure. Racers will often run into each other and fall to the ground without feeling the collision. The resulting humor is often very gratifying. In a scavenger hunt, one seeker could be reaching for an item only to have it disappear in front of his eyes when another seeker grabs it first.
Clever judges use Rings of Mutual Exclusion to allow all of the witnesses and suspected felons into the same room without them hearing each other. A guilty criminal usually becomes very nervous when the judge asks a potentially convicting question and the answer given is completely unheard. The guilty often break down and confess when witnesses don't have anything useful to say. The tension it creates is a very useful tool.