It all begins with a scream. Jack (John Travolta) is a sound technician working on a tawdry, low-budget slasher movie where the usual gaggle of photogenic teenagers gets hacked up by a knife-wielding maniac. The big problem for Jack is, the director doesn’t find the strangled, squeaky cry of the killer’s latest victim convincing enough. Jack and the director sit in the editing bay, glumly reviewing the footage, listening to the co-ed’s keening wail over and over again. Nope: it simply doesn’t work.

Jack’s quest to find a truthful-sounding, blood-curdling scream for the B-slasher provides the jumping-off point for Blow Out, director Brian De Palma’s mind-melting thriller murder, about political conspiracy and the power of the filmmaking medium. It also has what might be one of the most horrifying shock endings in 80s movies. I don’t mean horrifying in the sense of outright gore and violence, though Blow Out has more than a bit of that, as you’d expect from De Palma. No, Blow Out’s ending is horrifying in a psychological sense that hits you right between the ears; it’s the kind of conclusion that actively defies you not to sit bolt upright in your seat and say (or at least think):

“You can’t end a thriller like that. Can you?”

Yet as the credits roll, Blow Out leaves you to ponder what’s just happened. Jack’s final actions in the movie could be described as utter callousness, or more likely, the work of a man driven out of his mind by recent events and punishing himself by listening to the same piercing sound, over and over. The final scene could also be taken as an elaborate and incredibly twisted joke on the part of De Palma; a punch line to a gag which began with that first scream in Blow Out’s opening reel and paid off in its last. It says a great deal about the dark humour in so many of De Palma’s films that this latter reading is a remotely plausible one.

It was through thinking about my initial, knee-jerk reaction to Blow Out that I realised how carefully crafted and outright brilliant De Palma’s film is. I’d seen the movie before as a teenager, but I’d failed to understand the true gravity of that ending I’ve been talking about for two or three paragraphs already. Watching it again about 20 years later, I finally felt the weight and heft of Blow Out’s downbeat climax, its political cynicism and the totality of Jack’s failure in achieving the goals laid out for him as the film’s protagonist.

De Palma didn’t make matters easy for himself by giving Blow Out such a bleak conclusion (he wrote the screenplay as well as directed). When the film came out in 1981, audiences appeared to vote with their wallets, with the warm recommendations from critics falling largely on deaf ears. Yet De Palma remained true to the movie he wanted to make; in the final analysis, Blow Out’s conclusion is as vital to its construction as the desolate resolution of David Fincher’s Seven.

In fact, there’s another potential reading of Blow Out that its director may or may not have consciously placed there for us: the movie is a master class in how to craft the perfect shock ending.