When a cat feels safe and comfortable in its environment it rubs its head against the furniture, the corners of walls or the bottom of curtains, leaving a substance called the facial pheromone. It is specific to cats and conveys a message of security, reassurance and well-being. Feliway is a synthetic copy of this pheromone and is proven to reassure and comfort cats, helping them to cope with changes in their environment or other stressful situations. It's available as a plug-in diffuser (plug into the electrical mains) and that is what I am using, not just for Riley but for our two other cats.