It looks like an ordinary, gray-furred, white-footed field mouse a la Ramses ... except it's hugemongous! Its body is roughly the same size of a squirrel; I'd think it's a rat except that its tail is furry, not naked, and it's a light gray color rather than dark brown. It really does look like a mouse, except for being three times normal mouse size.
What do you think, folks? Is it a rat? Or is it André the Giant Mouse?
PS: An important note about Hitchhiker's Guide.