As the urban legend goes:
The Barking Dog
(http://www.eio.com/repairfaq/sam/humor.htm)
It is common practice in England to ring a telephone by signaling extra
voltage across one side of the two wire circuit and ground (earth in England).
When the subscriber answers the phone, it switches to the two wire circuit for conversation. This method allows two parties on the same line to be signaled without disturbing each other.
Anyway, an elderly lady with several pets called to say that her telephone failed to ring when her friends called and on the few occasions when it did ring her dog always barked first just before the ring. Pat proceeded to the
scene, curious to see this psychic dog.
He climbed the nearby pole, hooked his test set to the lady's line, and dialed the number. The phone didn't ring. He tried again. The dog barked loudly, followed by a ringing telephone. Climbing down the pole the amazed Pat found:
1. The dog was tied to the telephone systems ground post via a metal chain and collar.
2. The dog was receiving 90 volts of signaling current.
3. After several such jolts, the dog would start barking and urinating on the ground.
4. The wet ground now completed the circuit and the phone would ring.
I also dimly recollect the tale of a young scientist who avenged a tree that was faithfully watered by two posh neighborhood dogs. He had acquired a Van de Graaff generator or possibly a crank telephone. The generator was sitting in the tree, with a wire from each half running down the tree and exposed near the ground. When the dogs came near, owners in tow, he started cranking. The dogs urinated on the tree, unaware of the danger. Although most of the current would be trying to go down one wire and up the other, undoubtedly a portion found the path through the canine genitalia to ground attractive as well.
Looked at another way, this could be the hardware implementation of a protocol similar to RFC 2549, although more commonly ferrets are used to clear a blocked hamster packet FIFO queue.
| 
