Picture a pair of dancers looking like pale-faced zombies. They’ve been on their feet for days in the forlorn hope of winning a $1,500 cash prize that would lift them out of poverty. The rules are simple: don’t stop dancing. What they don’t realise is that the competition is rigged. Nobody is going to get any money.

Welcome to the Depression-era dance marathon that forms the backbone of Sydney Pollack’s 1969 masterpiece, They Shoot Horses, Don’t They? It’s a tough watch – intentionally so. The film, which the BFI is reviving as part of its “Discomfort Movies” season, refuses to offer audiences any consolation. At the point you think its two central lovers are finally going to kiss, the woman (Jane Fonda) gives the man (Michael Sarrazin) a pistol and asks him to kill her. Like someone putting an injured horse out of its misery, he obliges. The dance marathon goes on without them.

“It’s a metaphor, in a way, for American society, greed. And the desperation of people who don’t have money and privilege,” Fonda later said. Watching the film, we are in the same position as the spectators, taking a morbid pleasure in the extreme suffering of the participants – but also sometimes sharing in their stress and panic.