The Bread

Everyone puzzled over the new exhibit in the museum, A large floor to ceiling glass case surrounded a small three-legged stool that had a small, moldy piece of bread sitting on top. The description read, "The pitiful human race, waiting to be eaten and destroyed, but that hasn't happened. you were lucky. We were not." That was the simple part, the puzzling part was where it said, "It WILL soon be a reality. We are coming." The managers of the place said that it had appeared in the night, even while being under the watch of guards. How? Why?