In examining the implementation of a physical self-replicating machine on the Moon, we explore the implications of vertical closure as a constraint on the design of such. We describe the design of this self-replicating machine from its demandite list of in-situ sourced materials, a lunar industrial ecology to extract those materials, electrochemical and other chemical processes to purify desired materials and additive manufacturing methods for 3D printing the major components of the self-replicator. We then turn to the vertical closure issue defined through metrics based on resource-returned-on-investment, i.e. physical output/input ratios, and how this drives the design of the self-replicator. Several biological phenomena emerge suggesting that physical self-replicating machines can provide insights into biological life, terrestrial or extraterrestrial.