Illusion is a visual error. When people observe an object, because the object is subject to shape, light, and color interference, plus people's physical and psychological reasons, misunderstanding the object image will produce a judgment that is inconsistent with reality. According to the above definition, Which of the following are not illusions:. ['A mother who suddenly lost her son sometimes feels like seeing her son.', 'When sitting on a moving train and looking at the trees outside the window, I think the trees are moving.', 'People who are overweight will look slimmer in vertical stripes.', 'Cup Bow Snake Shadow.']