The process of spontaneous learning in an automatic food dispenser by a group of domestic female pigs was studied when one of the animals of the group had an aversive experience. Restraining a gilt in the dispenser without access to food resulted in later avoidance of the system by other gilts, especially when the reactions of the restrained animal had been especially violent and associated with urination. The hypothesis of a delayed transmission of an unpleasant experience was tested. The food dispenser was sprayed with urine collected from either a control gilt or from an animal undergoing stress. In half of the cases, the presence of urine of a stressed animal resulted in a long-lasting avoidance of the food dispenser, suggesting the existence of some kind of alarm pheromone produced in the urine of a sow during an unpleasant experience.