Pop Up Glass Sheets

Description
Pop up glass sheets are obstacles that you first encounter in Checkpoint 2. They spring up from the ground, or down from the ceiling. They are attached to a Metal, although only the Glass is a hazard.

Strategies
They can be easily smashed by:
 * 1) breaking a tiny hole
 * 2) throwing lots of balls (although this is a big waste)
 * 3) breaking a huge gap by dragging the balls across it. (the Dragging effect)

GIFs of them "popping" up or down
If you look closely, you can see the Metal holding the glass.

Trivia

 * They are encountered in Local Multiplayer Modes.
 * A similar variation is the Pop Up/Down Glass Panes. These go up and down according to the music.