People dress in cat costumes in celebration of the Festival of the Cats, also known as Kattenstoet, in Ypres, Belgium, on Sunday. The festival is held every three years on the second Sunday of May. The history of the festival dates back to the Middle Ages when people in Ypres brought in cats to kill mice and then killed some of the cats by throwing them out of Cloth Hall Tower before they could become overpopulated.Xinhua