Talking Skeleton

This happened down at my wife's store. As I have pointed out before, my wife has a store in a small Ohio town. The store has a lot of history having been built in the late 1800's. Halloween is fast approaching so naturally we have a lot of Halloween wares displayed for sale. Amoung the masks, critters, signs and other Halloween gegaws I have a six foot skeleton that is dressed in a tuxedo, black, with a white shirt and bright red bow tie. This skeleton talks in a low bass voice saying several different phrases anytime someone walks with-in six feet of him. His head turns, his teeth clack as he spouts his humor on often unexpecting shoppers. "Gabby" as we call him has been quite popular with the customers. As our store is small and we are in a small town there are periods of time when there are no customers. One of those periods, a short one, thank-goodness, occurred today. My wife was at the cash register in the front of the store and I was working in the work area pricing some late Halloween items. All of a sudden the skeleton starts talking. Being pretty certain there is no one but us in the store we looked up to see who got past us to get Gabby talking. There was no one there. We have "Gabby" situated midway back in the second room of the store. He is no where near a window or door. He only takes if someone walks in front of him less than 6 ft. He has never before ever talked unless someone activated him by walking in front of him. That was the only time today that is has occurred. There was nothing big enough in the store to activate him. Flies, bugs, and small rodents will not activate him. So what or who did activate him and how.