The New York Times has a great little short about ants, specifically their ability to both flow like a liquid and become a solid ball. It's kind of gross but also pretty awesome in how twisted the duality is. Look at it above. On the left, it's a thick, syrupy liquid. On the right, it's a tight rubber ball.
To flow, they moved around, rearranging themselves in the group, acting like a thick fluid. When the aggregation struggled to keep its shape, the ants clung to each other, acting like an elastic solid -- rubber for example.