Micro decisions can have macro consequences. A soft matter physicist reveals how interactions within simple cellular collectives can lead to emergent physical traits. Introduction Biofilms lead lives of liminality. Just a few cells thick, these layered communities of microbes anchor themselves to solid surfaces at interfaces — where rocks meet salt water in tide pools, between plants and dirt in root systems, or on the saliva-covered surface of your teeth. Amalgamations of single cells, biofilms...