Emily is watching Bob as he stands at the bathroom sink brushing his teeth before going to bed. (Okay, what she's really doing is staring at and admiring his butt and legs, something she still loves doing even after nearly fourteen years of marriage.) While doing so, she notices that the left side of his lower body seems to be slightly more muscular than the right side -- not in any sort of grotesque way, but there is definitely a difference if one looks with an observant eye. She wonders why she never before noticed this.
Emily: You know, your left leg is slightly more muscular than your right, which is odd, because I'd think you'd be right-legged.
Bob: No it isn't. [He knows because he's got such a good view of his back legs, standing in front of a sink with no full-length mirror in sight.] What are you talking about?
Emily: It is. Just slightly.
Bob: It's just the way I'm standing and the way the light's casting shadows or something.
This explanation does not satisfy Emily. She knows what she sees, and it has nothing to do with posture and lighting. However, she's been married long enough to know that the wise thing to do at this moment is to let the whole thing drop.
Emily: Oh yeah. Maybe you're right. [Yes, even ministers' wives are known to lie in order to keep the peace.]
Nevertheless, just before she falls asleep, she's thinking about this conversation again. Why would Bob's left leg be more muscular? Then she realizes: he's got plantar fasciitis (a runner's problem that basically affects the heel of the foot, sometimes causing great pain). She always forgets which foot it is, but she bets it's the right one, that through favoring it, he's giving his left leg a bit more of a workout when he runs and walks.
The next morning, Emily is busy writing. The phone rings. It's Bob.
Bob: You know, I've been thinking. Maybe my left leg is slightly more muscular than my right. My plantar fasciitis was bothering me this morning, and I realized I put less weight on it and more weight on the other leg when I'm walking around.
Emily: That's what I was thinking last night, too. The plantar fasciitis is in your right leg, right?
Bob: Yes. See what a good detective you are? This is why you ought to be keeping all your options open when you think about what your next career move is going to be.
Emily: Don't be ridiculous. I'm not suddenly going to become a detective.
Bob (the smile in his voice is obvious): Why not? I can just see your ad in the paper: Emily the Detective. You can pose with Francis [the cat] as your sidekick.
Detective? No. Writer of detective fiction? No, not that either. Wife who keeps her husband on his toes? Now, there's a career I'd consider if someone would offer to pay me good money...