Bacteria must sense a surface to colonize it. Surface sensing helps establish thriving biofilms that can pose significant threats to public health. Bacterial mechanosensing – which involves the sensing of mechanical resistance (for example, increased viscous drag) – is widely believed to aid in surface sensing. I will briefly discuss the current progress in the field and explain how numerous studies have misattributed surface sensing to mechanosensing. I will discuss an alternate hypothesis involving the sensing of metabolites that are endogenously-produced. One such metabolite produced by our gut microbiota is indole, which serves as the first line of defense against invading pathogens. Consistent with this notion, our recent work shows that indole strongly repels chemotactic bacteria, causing them to migrate away. Why does indole not repel our own microbiota then? I will attempt to answer this conundrum by explaining our discovery of a bipartite metabolite response in bacteria.