Algodoo

Just something I've created by spawning hinges at collision. Description in scene. Yay I like that spawning method Mayby I put there some herbivores or something Feel free to use it.

Since you say you don't know what to do:
The little circles in the boxes under the big red box (the green, the red, the color changing and the blue) are just initiators. When you press play the yellow circle that collide with the black box (that are 2 circles in real) creates 200 green circles that fit in the red area. They are kinda prepared so the initiators can give them their code and this code should work well in the green circles. Now if you drag the "infected" balls and collide with them with the green circles (that appear after sim start) the green circles'es code and color will change into the code and color of the infected ones. On collision they also are connecting to each other by creating a invisible hinge. Infected circles don't connect to other infected, only to green - so if you drag the "alge" (it looks like an alge! i'll edit the scene to show you a big alge) through the green circles field it'll grow. If colideing with dark boxes it'll stick to them. Just play around with the scene.
I just thought it can be useful for someone so I added it on algobox.

I don't know why it doesn't work on algodoo, but you can download Phun (it's free ). I use Phun

Please read the advices in the boxes - everything is explained there.

You just have to usethe drag tool. If you want to spawn a new 200 green balls simply drag the blue circle into the "Reset" box.

If it doesn't work try typing id=200 ; x = 0 ; y = 0 and colori = [1.0, 0.0, 0.0, 1.0] in the console (F11). I don't know what I can explain more. If anything isn't clear for you just ask.

Edit2:
I just added a very simple but usefull function:
A destroy key for the spawned circles (works also after color change or anything else). It's "D". To hide the hints press "H"

That are only algea guys...