In a moist, well-aired compost heap, billions of bacteria and fungi break down garden and kitchen waste, giving off heat as they go. At the core, temperatures can climb to 60 or 70 °C (140 to 160 °F) for several days, enough to kill many weed seeds and germs. It takes enough volume, around a cubic meter: a small bin loses too much heat and stays cooler, though it still does its job.
Chlorine on its own is fairly gentle. But when it combines with urine, sweat and other grime from swimmers, it forms chloramines, which cause stinging eyes and that classic 'chlorine smell'. A well-kept pool barely smells at all. Shower before you swim and never pee in the water.
Muscle mass slowly shrinks with age, putting independence at risk. But in 1990, a study had nursing home residents aged 86 to 96 train their legs for eight weeks: their strength more than doubled. Muscle responds to training at any age. Getting up from a chair without using your hands is already an exercise.