Over the months he's spent living with the Mouri family, Conan has developed a somewhat accurate sense of the (as Ran calls them) "moments" that come and go between her parents. Sometimes during a case he'll miss it, but when deductions aren't clouding his mind he can tell that something else is going on.
Even if he's not quite sure why. Kisaki-sensei seems too logical to seriously want to get back together with Kogoro, the boor that he is.
Then again, feelings are hardly logical. Not everyone can be Holmes, escaping the chains of emotion. Which raises the question...
Leaning across the table, Conan chirps, "Ne, ne, Kisaki-sensei!" She looks up from the meal Ran prepared, the first time she's let her eyes go across the table, to where Conan sits next to Kogoro. "How did you and Ojisan get together?"
The response this prompts is unexpected. Kisaki-sensei gasps and flushes a dark red, Kogoro chokes on the mouthful of rice he'd just eaten, and Ran shrinks down in her seat, saying "C-Conan-kun!" reproachfully. There's a hint of a smile in Ran's expression, though, which makes Conan think he's done something right.
"Whaaaat?" he asks petulantly. "I was just curious..."
After a moment of carefully not looking at her husband, Kisaki-sensei sighs. "Well," she begins, staring out the window, "I suppose it started in high school. We'd known each other for years, but it was then that he first really started to - to irritate me."
"O-oi!" Kogoro shouts, automatically defensive. "No more than you irritated me!" Ran winces at the noise, but Conan doesn't think the kind of fight she's expecting is coming.
"How did irritating you make you like him?"
Kogoro grunts, agreeing with the sentiment behind the question, which gets Kisaki-sensei's attention. Making eye contact brings a high flush to her cheeks again, but neither of them look away.
"Ah - well - I suppose it wasn't really irritation, so much as..."
"As?" Kogoro prompts, face and tone deadly serious. The mood of the room has changed in the space of a moment, from embarrassed anger to... something else.
As Ran tugs him away from the table and into the kitchen to watch excitedly, Conan can't help but wonder how a simple question led to another of Ran's so-called "moments". He'd just been trying to gather some evidence, to make sense of why those moments keep happening. He hadn't been looking to cause one.
Though... looking at the two of them, red-faced and smiling slightly as they reminisce, he can't say that he minds.