On startup you enter the debug mode in spectator view. This can be change with "/gamemode 1" to creative view.
When you step on any of the 4 not activated pressure plates it will spit out a ton of that pressure plate you're on, slow down minecraft and make some weird noise.
If you step on an activated pressure plate nothing happens.
Environment
OS: Windows 7 (ver 6.1, amd64)
Java: 1.7 Update 51 (by Oracle Corporation)
Launcher: Minecraft Launcher 1.4.4
Minecraft: 14w27b
Dupe of MC-58898