Which visual indicator suggests a glass is NOT "beer clean"?

The correct choice indicates that when bubbles adhere in a uniform pattern on the surface of a glass, it suggests that the glass is not "beer clean." In a properly cleaned glass, bubbles should typically not stick to the sides but rather rise and either burst or become detached from the surface.

When bubbles cling evenly, it is often a sign of contaminants or residues, like oils or soap, which can negatively impact both the appearance and the aroma of the beer. Such residues affect how the beer interacts with carbonation, leading to a poor head retention and an unappealing experience. In contrast, the other answers describe conditions that are associated with a clean glass, where bubbles do not cling or form an inappropriate layer.