Ferrets are very good at getting into holes in walls, cupboards, or behind household appliances, where they can be injured or killed by electrical wiring, fans, eating foam rubber, and other dangerous items. Fold-out sofas and recliners are very dangerous for them, since they will often climb inside the springs and then be squashed to death. For these reasons steps are often taken to "ferret-proof" a home before acquiring one as a pet. Ferret-proofing a house often involves removing items dangerous to ferrets and covering over any holes. Many owners opt to restrict the ferrets to a cage at night or when there is no one home.