"How could it be possible that there were farmhouses in the middle of the mountain side? There were no roads of course; sometimes not even a path. Still they have cattle, and cattle would need food. Hay. The answer was the transport wire.
"By a well-developed network of transport wires they could move anything (even the cattle itself) up and down the mountain sides without trouble. Once established, this system generated a whole culture of its own. Since the length of the wire could exceed the range of the human voice, signals would be needed. 'Sla pa traden' (from the Norwegian language) means literally to knock on the wire, and that is precisely what was done.
"Different 'codes' for every need gave a large number of signals. Though modern agriculture no longer gives room for such methods of small scale cattlery, this system is still alive in some rare places in Norway. Later in history, when the telephone spread to everywhere, the expression transferred to that new system of wires. Nowadays, 'sla pa traden' is a commonly used phrase in Norwegian for using the telephone."