If you are unable to simply reach down into the wall and retrieve the critters, you will need to cut a hole in the wall where they are trapped. Unless you are an experienced DIYer, this will likely mean calling a wildlife removal professional.
What animals get trapped in walls?
Wild animals often live in homes. They most commonly like to live in the attic, but sometimes they will crawl down the walls. Other times, they fall down the walls, and then get stuck. The most common types of animals in walls are rats, mice, squirrels, raccoons and opossums.
How do you know if something is living in your walls?
Pests have surprisingly strong teeth and can gnaw their way through lots of different materials in your home. If your insulation looks like it's been disturbed, or your floor trimming has a few bites taken out of it, then you definitely have something living in your walls.