By approximating the creatures as a circle (sort of like the old ‘assume a spherical chicken‘ approximation back in our engineering skule days), the end result looked kind of cool, as the effect resembles a little blob swimming around a pool with other blobs, inanimate bricks and circle objects.
Using the physics, one can also use the mouse (or touchscreen on the smartphone) to drag and throw around the objects and watch them fly around the screen to hit other objects in a self-consistent way. This is accomplished by connecting a ‘spring’ object to the object and the point where the mouse is released.
I have also made the creatures in this version animate, in the way the try to reynolds-style steering behaviour (also driven by a system of hidden box2d-springs). The end result is if a little creature gets smacked by a large object and flies around, it will try to swim back to its original direction it ‘wants’ to go, and not necessarily follow the direction of the smackin’.