Sliding Glass Panes

Sliding Glass Panes are an obstacle frequently encountered. They are not much of a danger when slow, but are a huge hazard when fast. They also have a counterpart which shifts instead of slides, the shifting glass panes.

Teaser
In Mediocre's teaser blog "First screenshots of Smash Hit!", one of the pictures has a Sliding Glass Pane being smashed. A description of this fake checkpoint can be found at Introductory Stage or Introductory Stage (Teaser).