A couple of our landline extensions stopped working recently. Son tracked down the problem (photo below) inside a ventilation duct. A rat or mouse had stripped the outer sheathing, chewed the wire insulation over about 100 mm and even managed to severe 5 of the 8 wires!
An electrician installing new wiring several weeks ago had warned us a data cable in the duct had been attacked by rodents. Didn't realise it was so bad or would fail so soon.