maggiesensei.com/2009/08/11/%e3%81%86%ef%bc%9a%e3%81%86%e3%81%9d%ef%bc%88%e5%98%98%ef%bc%89%e3%80%80/
Japanese often use “うそ ( = Uso ) when they are surprised, like ”Really?” “Are you sure?” “No kidding!” No way!” or when they hear something unbelievable or unexpected.