How do you know if you've got a racoon or possum in your house?

Raccoon's make trilling noises and destroy as much as they can. An opossum will make very little mess and as far as I've heard, they only hiss. When I had a playhouse, a mother opossum had her babies in my Daddy's army trunk. I never knew they were there until I opened the trunk to put something in it. Mom 'possum just hissed at me. It was enough, if you see all those teeth and you're only 3 years old, you leave quietly and tell Daddy he needs to clean out his trunk. My Dad said to leave them alone, and Mom 'possum would find a new home for her babies. She did, they were gone the next day.