An electric pulse (current) will travel from the energizer through the live (hot) wires. The current flows through the animal at its contact point on the fence. The current then travels into the ground and will seek a return path via the earth spikes back to the energizer. This completes the electrical circuit and the animal is shocked. The circuit is completed almost instantaneously. The shock creates an unpleasant memory and thus a psychological barrier that most animals recall very quickly and for a long period of time. Different animals require different levels of shock or energy, the level is not based only on the size of the animal but also on the temper and type of animal. Once the animal has been shocked chances are that it has learnt its lesson and it will avoid the fence. An electric fence does not have to be very robust but it must rather be visible to the animal so that the animal can see it to avoid it.