[[WMG: The mouse is [[Literature/TheGreenMile Mr. Jingles]]]]
It's obvious the mouse in this movie is not only smarter than the average mouse, but also very old; much older than a real life mouse can live. The house came into Mr. Smuntz posession years before the events of the movie, and the mouse had already driven out the previous owner by that time. ''The Green Mile'' is set in 1932, this movie in at least the 1970's, and the epilogue of the Green Mile in the 1990's. That leaves enough time for mr. Jingles to have ended up in the house after the events from the Green Mile, lived there for several years, eventually fighting and then befriending the Smuntz brothers in the 1970's, before making his way back to Paul Edgecomb in the 1990's.
* I love this, make it canon.
** To do that you would have to own both ''The Green Mile'' and ''Mouse Hunt'', but you can make it fanon.
* Well, it could a relative (brother? son?) of Mr. Jingles, and the old house their family home. Maybe this mouse was just watching it on behalf of his kindred.
[[WMG:The mouse is Mr. Smuntz.]]
To follow up on the implication made under HiddenDepths on the main page: while obviously this could not be the case from the start (the mouse lived in the house for decades or even longer, at least a good portion of which was while Mr. Smuntz was alive), the fact that the mouse knows how to make the Smuntz's incredibly unique signature sandwich, that in the end it seems to be interested in trying to help the string factory become successful again, that unlike with Caesar and the house's previous owner the mouse ends up joining forces with the brothers to achieve a happy ending for all, and that mice are said to be able to receive a dead person's soul, all suggests that Mr. Smuntz's soul passed into the mouse upon his death. Note the implications made that Mr. Smuntz himself was something of a trickster; that despite everything which happen to the brothers they never die or are too badly injured; that destroying the house wouldn't matter to him since he never used it when alive and it was only the factory (and his family) he cared about; and that everything which happens could be interpreted under the guise of trying to get the brothers to learn to get along and join forces for the betterment of themselves and the business--i.e., that the mouse too was trying to teach them "teamwork and sharing mean everything".