Compostcubator 0.4 uses a compost system as incubator – a compostcubator – to provide the necessary heat to maintain a small flask of disembodied mouse cells. An incubator simulates a body. It acts as a homeostatic surrogate for life out of context, out of place, and out of agency. This project complicates this apparatus by making it into a living system – a messy ‘biological device’ that is an assemblage of different species. Built from a metal frame, wire mesh, five tonnes of locally sourced mulch, horse manure, and beer barley waste, the compost generates heat as bacteria decompose the biological waste. Inside the compost a 100-metre coil of plastic tubing contains water. This water is heated by the process of microbial decomposition and pumped to a custom-designed incubator made of clear acrylic and copper. The work plays with and critiques notions of control, optimisation, kinship, interdependence, and multispecies ecologies.