Even though you may think you know where the ferret is, never assume. Many ferrets have died that way. Regular couches also need to be ferretproofed. Ferrets can get inside the couch and crawl up in the springs, and come to an unfortunate end. Look around your house to see if you have anything like this.
Ferrets like to chew on leather, plastic, and rubber.
This can be a very bad thing if the object is small, and the ferret swallows it. Blockages are life threatening to a ferret. Ferrets can also get their heads stuck in toilet paper rolls, so it is a good idea to tear them up before you throw the empty ones away. Once in a great while a few ferrets will even chew on electrical cords which is very bad. A little coating of bitter apple or Tabasco sauce will usually cure this, however.