During a recent lunch in a restaurant, someone complimented my wife on the perfume she was wearing. But I was wholly unaware that she was wearing perfume, even though we had been in a car together for about half an hour, driving to the restaurant.

My sense of smell is very poor. But there is one thing I can smell far better than most people — gas escaping. During my years of living on the Stanford University campus, and walking back and forth to work at my office, I more than once passed a faculty house and smelled gas escaping. When there was nobody home, I would leave a note, warning them.