The most obvious place in which to start looking at what chemistry might be is with the standard – ahem – conclusion of the romantic relationship: Sex. Sex is at the heart of the most classic definition of ‘chemistry’; cinematic history is ablaze with couples whose interactions make it clear that whether we see it or not, sex is what is – or what soon will be – happening. Clark Gable and Vivien Leigh in Gone with the Wind, Patrick Swayze and Jennifer Grey in Dirty Dancing, Hugh Grant and Andie MacDowell in Four Weddings and a Funeral, Tom Hanks and Meg Ryan or Emma Stone and Ryan Gosling in pretty much everything else between them – these are just a few of the many pairings who have a particular something between them that makes the audience themselves root for things to go a certain way. For some reason, their relationship means something to us.
But these examples are the easy part. The theory that sex is the Bunsen burner (seriously – I’m sorry) of character chemistry explodes surprisingly easily when we look at the uncomfortable – and often pretty entertaining – fact that there are just as many examples of when sex just doesn’t, as it ‘were, work. Hayden Christensen and Natalie Portman in Star Wars: Episode II – Attack of the Clones are probably most often held up as ‘the-couple-with-the-least-chemistry-in-the-history-of-not-just-film-but-quite-possibly-the-world-ever-including-between-all-family-members-and-members-of-warring-tribes’ and it is sadly true; there is simply not one iota of believable connection between them. One has to assume that we only got Luke and Leia at all because Varykino made its own wine.
Johnny Depp and Angelina Jolie are also infamous for setting the screen on barely a mild glow in The Tourist, with two performances that suggested neither was sure if the other was even a human being, let alone an attractive member of the opposite sex. Christopher Nolan must have thought that Christian Bale and Katie Holmes were exuding so much chemistry in Batman Begins that they were in danger of overshadowing the rest of the film – as he promptly recast Holmes’ role for The Dark Knight. Carrie-Anne Moss and Keanu Reeves had an actual onscreen sex scene in The Matrix Revolutions, which was quickly added to many people’s lists of things in life we dearly wish we could unsee.