Life is all about making choices. This applies as much to tiny worms as it does to humans. Despite the difference in these two animals’ life styles and brains, their decision-making process shares some fundamental properties: trade-off, and deliberation followed by commitment. To address how brains perform such decision-making processes, we take a reductionist approach: to identify circuit motifs which function as minimal computational units and that can be found in the brain of any animal. For this, we combine automated analysis of behaviour, neuronal manipulations and modelling to dissect the C. elegans male’s choice between sex and food.