if you put a dead animal in the freezer, wrapped in a plastice bag, lay the dead animal on top of the other
Anything you store in the freezer needs to be airtight, or odors will propagate. And they'll linger in the freezer itself, not just the other food, so you really want to avoid this.

If you're using plastic bags to store things in your freezer (and they're not zip-seal bags), make sure they're thick and tied off airtight. No harm using multiple bags to make extra sure!