"We're subliminally relaxing you."

Taking a cue from retailers, casinos often circulate oils and scents into their ventilation systems to try to put gamblers in a good mood. In 1991, the Mirage Hotel and Casino in Las Vegas started circulating the smell of coconut butter on its property to match the casino's tropical resort theme. At 500,000 square feet, the gaming/hotel section of the Mohegan Sun complex in Uncasville, Conn., is the largest scented building in the world. It has more than a dozen different smells circulating within its walls, says Mark Peltier, cofounder of AromaSys, the firm that installed the system. The Venetian casino in Las Vegas, also an AromaSys client, circulates an array of herbal scents, including lavender, throughout the casino floor.

Why the olfactory overload? It's generally believed that people will stay longer — and therefore spend more — in a place with a pleasant smell, says Peltier. Lavender aromas, in particular, have been clinically proven to induce drowsiness and promote relaxation, says Wendell Combest, a professor at the Shenandoah University School of Pharmacy. The scents have no known harmful side effects, but be aware that it might be more than just the free drinks making you feel so happy-go-lucky.