Minecraft wiki entry for Rube_Goldberg_machine, associated text: Placing a one tick piston, or a liquid flow, that pushes away the torch in front of it that has gravel on top can be useful. On this gravel, there is a torch on the side holding up another gravel, etc. You could even make a message with these, by stacking gravel and sand, to write something like "THANKS FOR WATCHING". This isn't visible when in its "torches" state, everything falls into place.