Electrically speaking, back in olden times of party lines etc, the ringer in the phone was connected between the ground and Tip or Ring. So each phone had a red, green and yellow wire. Two wires were not good enough. You needed the yellow ground wire or the ringer would not work. On a two party line, one ringer would be on tip to ground with the other ring to ground so each party only heard their own ring. There were other methods of making you only hear your own ring as well, frequency selective ringers were a popular method.
With the ground wire broken and connected to the dog, the 90 VAC 20 Hz ringing current had to pass through the dog for the phone to ring. Two wire phones in use today use what is called bridged ringing where the ringer is connected to tip and ring. But I will bet that if you connected a phone or a ringer from ring to ground it would still ring.
