That grey-green rim around the yolk is iron sulfide. When an egg cooks for a long time, the white releases sulfur as hydrogen sulfide, which drifts toward the yolk and meets its iron. The longer the cooking and the slower the cooling, the darker the ring. It's harmless, but easy to avoid: cook for about ten minutes, then plunge the egg into cold water.
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.