It's a natural instinct that ferrets have that they hoard and hide things.
Ferrets hide things because of the natural instinct to hoard things.
For example if they kill something such as a mouse or anything else to eat and they eat only half of it then the ferret will hide the rest of the mouse to eat later on.
Ferrets even as pets hide household things because it's an offshoot of stashing away prey animals they've caught in the wild.
It's just a normal thing they do and that they are used too doing.
Sometimes ferrets will take off with things you don't want them too and hide them and it can be hard to find the things they hid.
So make sure to keep things up and away from your ferret if they are out of the cage.