Mary Businge was in the doctor's seat, diagnosing a patient, when the municipal workers arrived. They were in a foul mood as they rolled up their sleeves and descended into a trench filled with sewage. The trench, stretching across the Nankulabye slum in Uganda's capital city Kampala, was where the slum's roughly 40,000 residents dropped their waste: discarded cans, torn shoes, playing cards, cigarette butts, documents, sanitary napkins, and bags containing feces. When it rained, the acrid water rose like a breathing thing, and so the city government sent their workers to empty the trench.