To draw glass, the game's graphics programmer Alex Evans borrowed memory meant for smoothing jagged edges, so each pixel had room for two layers: something solid, and one see-through thing in front of it. But, as he put it, two is not a big number: put one pane of glass behind another and the one behind has nowhere to go. It vanishes.

Players turned that into a trick. A thin sheet of glass across the front of the whole level fills every pixel's see-through layer, so every glass part behind it disappears: the rods, the pistons, the wheels. Only the solid parts still show, and platforms ride invisible pistons. Evans called them "magical" levels, and added: "In the hands of the right users, no mis-feature is ever all bad."

The level, machine and glass in this film are our own simplified version, built in code. Not affiliated with or endorsed by Media Molecule or Sony Interactive Entertainment.

Which game's happy accident should we open up next?

Sources: Alex Evans (Media Molecule), LittleBigPlanet graphics engine postmortem, SIGGRAPH 2009 (Advances in Real-Time Rendering course), slides and speaker notes.
Sounds: our own, made in code.