
It's an odd thing, chemistry. Some movie couples have it; some don't. What fascinates me is when real life couples appear together as romantic leads, some simply don't have it. I've previously posted about how marvelous William Powell and Myrna Loy were as Nick and Nora Charles in The Thin Man series and how, in comparison, his real-life wife Carole Lombard and he didn't click nearly as well in My Man Godfrey.
Of course, even if real life couples are able to make the screen sizzle, sometimes their marriages falter. Consider these examples:

One of my very favorite couples, Emma Thompson and Kenneth Branagh, had fantastic chemistry in the aforementioned Much Ado as well as the superb version of Henry V.

They also starred together in one of my all time favorite little-known mysteries, Dead Again, loaded with twists and turns:

Chemistry is tricky. I'm reminded of Justice Potter Stewart's attempt to explain "hard-core" pornography, or what is obscene, by saying, "I shall not today attempt further to define the kinds of material I understand to be embraced . . . [b]ut I know it when I see it . . . "
These three couples had chemistry. Sometimes it was like adding vinegar to baking soda, bubbling merrily along; sometimes it was more like adding Mentos ® to Diet Coke ® - explosive. But it was always a blast to watch.