For those who aren't familiar, "smell-the-fart" acting is basically a reference to Friends and that one time he taught an acting class.
Forget method acting, forget Stanislavski - the single, best way to accurately portray suspicion on screen is to pretend that someone let one rip. Considering last night's Graham Norton couch was essentially a who's-who of acting talent, Kenneth Branagh decided to lead the cast of Murder On The Orient Express on a quick, improvised scene.
Except seemingly someone actually did fart and it might have been Dame Judi Dench. Do they change the covers on the couch after someone farts on that couch? Just give a second and think about the thousand of asses on that couch.
The law of big numbers - Google it - means that somebody, at some time, let one off in the middle of filming. What are the odds it happened that night and people actually were smelling the fart?
Take a look and judge for yourself.