A yellow face with open eyes and a skewed frown, as if scrunching its cheeks or chewing its lips. A look of feeling unsure. An Google’s design heightens its intended puzzlement by including contorted eyebrows.
While it can convey confusion, it is commonly used for moderate sadness, disappointment, and frustration, thanks to its frown.
Samsung previously included raised eyebrows, as did Microsoft along with a rotated S-shaped mouth, à la the :S emoticon.