One of the worst experiences you can have is to head out to your garage after winter, open the door to your classic Corvette, and smell the unmistakable odor of a mouse.
In this case, the mouse didn't roar; he sighed contentedly. What you're smelling is the mouse's urine, which has probably been deposited all over your carpet and seats. Like most urine smells, this ain't going away soon, even if you manage to evict the mouse (or mice) from your car.
Getting rid of mouse smell is hard, even though the steps are easy to describe. The first thing to realize is that half-measures simply will not do the job. You can't sprinkle some carpet-fresh around or hang an air freshener from the rear-view and expect results. Mouse urine is the gift that keeps on giving. Cat urine - if that has happened to you - is even worse.
This topic came up recently after I purchased a 1969 Corvette that had been left for a year in the previous owner's garage. From the time I walked up to the car, the smell was overwhelming and the recent dusting of carpet-fresh told the story. But I bought the car anyway, because more was right with it than was wrong, and I knew I'd get this story out of the experience.
Note: Play it Safe
Note that in many parts of the United States, mouse droppings may contain hantavirus. Wear a respirator and rubber gloves, and immediately dispose of the mouse nesting materials and any droppings you find. You don't want that disease, and more importantly, mouse yuck is simply gross.