"Doctor, I understand that I have kidney problems, but why does it lead to headaches?"
The patient looked confused. "I get it when you say I have symptoms like dizziness, tinnitus, weakness in the waist and knees, and frequent dreams, but why the headache?
"Moreover, it aches whether it's hot or cold, especially when I'm working or when I'm... intimate. That's what I don't get."
By this time, Du Heng had figured it out and was quite relaxed, so he started to explain patiently, "Think of your body like a car engine. For it to work properly, running long distances or carrying heavy loads, wouldn't you need to maintain it? Wouldn't you need to add engine oil from time to time?"
The man nodded blankly, not sure what Du Heng was getting at, but listened attentively nonetheless.
