By analogy to cells that grow, split, merge, and die, this paper applies same operations to things residing in an open Internet-of-Things (IoT) ecosystem. Despite the growing interest in IoT, things are mainly “busy” with sensing and (some) actuating, which prevents them from being responsive to changes in this ecosystem. To address this limitation, this paper proposes mutation as a novel mechanism for making things responsive and hence, capable of either satisfying “unseen” needs or seizing “unexpected” opportunities. To approve/deny mutation, a decision-making process is initiated progressing over 4 stopovers (obligation, permission, prohibition, and dispensation) along with 4 stages (awareness, pre-mutation, mutation-itself, and post-mutation) that would allow to answer questions such as why to approve/deny mutation, how to prepare mutation, and how to evaluate mutation. A testbed demonstrating the technical doability of thing mutation along with the conducted experiments are also discussed in the paper.