Scratch

A while ago I saw http://en.wikipedia.org/wiki/Self-reconfiguring_modular_robot , and found it interesting. Then, after a few days, I thought that since in Scratch, you can copy sprites with the click of 2 buttons, "Could someone make a sprite, when duplicated many times, form a many-sprite structure by itself?" Now that I have a Scratch account, I can ask it here!

Credit in my sig and love it for whoever makes the best one!

Rules:
1. The sprite must be one sprite.
2. It cannot have any access to any global varibles/broadcasts.
     2-info. You can only have a sprite with "pixel-sensors", and monitor them with "If color _ is touching _" blocks. If you ask "How do I let different sprites communicate", simple! For example, make the body have about 3 or 4 colors, and use it to communicate with binary code, for instance.
3. Don't let the bot move too fast, 1 or 2 pixels per loop is enough.
     3-info. You could use decimals like move 1.3 steps.
4. No numbering (like having a "Set VAR to #" at the beginning of each script, and using them as IDs.)

(It will be a top down view)
MAIN RULE: Make it as close to real life as possible.

Goals (not in any particular order) The more you satisfy, the better the bot will be.
1. The bots should form a many-sprite structure when left alone.
2. The bots must obey walls.
3. When one bot is given a specific signal (changing a local varible in one bot), all the other bots should be able to follow it. (ex. I give one bot of a line-multi-bot a "SQUARE" signal, and the bots all form a square)
4. Use a mininum of varibles, scripts, sensors, costumes, reconfiguration time.

Post if you need clarification!