There's only one reason Michigan-Minnesota is any more of a rivalry than, say, Michigan-Wisconsin or Michigan-Indiana (which aren't really rivalries at all): the Little Brown Jug.
Some background: The jug was left behind by Michigan after a 6-6 tie at Minnesota in 1903, and when UM coach Fielding Yost wrote to request its return, he was told that Michigan would "have to win it." They did so six years later, starting a rivalry that still exists today. The unusual thing is that there's no particular animosity or regional tension between the two schools -- the rivalry exists because of the jug, not the other way around.
When Greg at MVictors started putting together a mini-series on the history of the jug, he ran into an unexpected question: Is the jug in use today the same one that was left behind in 1903? According to Lloyd Carr and UM spokesman Bruce Madej, no. According to longtime Michigan equipment manager Jon Falk, yes. I honestly didn't know there was much of a debate; the thing looks old, and it seems like there'd be a great story behind its loss/destruction/replacement if the original was no longer around (although if it was replaced in like 1937, who would ever know the difference?)
But Greg wasn't willing to settle for the old "I guess we'll never know" conclusion, instead embarking on a mission that led him from UM's Bentley Library to the Henry Ford Museum in Dearborn and back to Schembechler Hall for a MysteryQuest-style investigation. I'm talking about serious research here -- the Internet is full of crap, but if there was a Pulitzer Prize for sports trophy investigations, this would win.
So ... has the jug pictured above been around since 1903? Read the story and find out.