The Little Brown Jug is the oldest football trophy in all of college football, so naturally most of what you think about it isn't true. Michigan Coach Yost didn't really buy the jug out of fear Minnesota would try to poison their drinking water. Similarly Gophers Athletic Director Dr. Cooke probably never refused to return the jug to Yost, making him win it back.
To illustrate this let's look at the first known article about the jug, from February 7, 1904 in the Minneapolis Tribune:
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Was Brought From Ann Arbor Filled With Michigan Water for Use of Wolverines During Football Game—Was Forgotten After Contest and Now Reposes In Dr.