When humans first arrived on the planet, the wild nighthorses were immediately drawn to them because of the humans' unconscious sendings that were rich in images and emotion. Once a nighthorse has experienced such sendings, it becomes addicted to them and will not leave humans alone. Sifting through these human emotions, a nighthorse will eventually select the human whose sendings it likes best and will adopt him or her as its companion. It will follow this person around, and if he or she is in a village or town, it will remain close to the walls and "call" by flooding the person with images of itself for days and weeks on end until either that person relents and goes to the horse, or withdraws to the centre of the town (if this is possible) where sendings from the Wild generally do not reach.