Blooper or gag reels - with line flubs, prop malfunctions and clowning around - during movie end credits or as DVD extras are relatively commonplace nowadays. They're a bit of a giggle for audiences and show them that actors are human too! And what fun they had during the making of the movie!
They're generally found on comedy films: seeing actors flub their lines beside the end credits would rather break the spell of, say, Schindler's List.
And they've also been found on TV compilations of film and television bloopers such as It'll Be Alright on the Night.
But the enjoyment of movie boo-boos goes back a long way. Obviously bloopers go back a long way but most Hollywood studios in the old days seem to have trashed them, though the odd snippet might have been smuggled out for private enjoyment.
A studio like Metro-Goldwyn-Mayer that took itself very seriously as the biggest and the best would not want its stars to be tarnished by appearing to be less than perfect. But no doubt such mistakes were captured on film, even if not screened (at least not publicly).
Warner Bros, with its slightly more raffish image, seemed more willing to laugh at itself and made something of an art of the blooper reel. Examples can be found online and on some of their DVD releases.
Bloopers were kept and between 1935 to 1949 compiled into Breakdowns of [year] and shown annually at the Christmas parties run by the studio's social club. Sometimes the bloopers would be grouped by stars, and repetition, sound effects, specially produced animation, and other tweaks would add to the fun.
Watching them now is an interesting experience given the self-possession and precision we associate with old-time stars and their films. How they react to mistakes - their own or others' - provides a glimpse of the people and the process behind the high-gloss mystique and brings them closer to the slightly less elevated Hollywood of today.
It's worth remembering actors in the studio system worked hard, some making several films a year, so the pressure to get it right and keep production going was high. But having to learn lines rapidly was also hard so it was inevitable mistakes occurred.
Ardent film buffs will recognise most of the films and stars but many of the actors, at least, are still familiar faces. There are moments from classics like The Big Sleep and The Adventures of Robin Hood. Contracted or on-loan stars like Errol Flynn, Ronald Reagan, Edward G. Robinson, Claudette Colbert and James Cagney are among those who pop up and stuff up, to everyone's amusement.
Humphrey Bogart and Bette Davis are two notable repeat offenders: The reason is unclear: maybe they were more fun to needle with reminders of their gaffes or more prone to error.
Despite the fact the bloopers were for private showings, some of the earthier language seems to have been amusingly covered by sound effects - some non-actors at the studio must have had delicate sensibilities - but other words and phrases do get through, repeatedly.
The rather quaint "Nuts!" is a frequent exclamation. "Damn!" "Goddamn!" and "Goddamnit!" "Hell!" and "Son of a bitch!" are also frequent. Davis among others can combine them - "Nuts to that goddamn line!"
Sometimes the actors garble a line, sometimes they forget it. Sometimes the snafu might not be their fault: there could be trouble with a costume or a prop, or a crew member might come into view.
And sometimes people just get the giggles, or prepare a little gag to provide some amusement for themselves and their colleagues - like two men breaking into a waltz and a third cutting in, all in good fun.
Some actors seem genuinely annoyed at themselves when they mess up, like Bogart, while others, like Robinson, seem to laugh it off more readily. And sometimes the sound of those offscreen laughing - the director, crew members - can also be heard.
Stewart, in one clip, seems taken aback when a shot continues as he walks off - "Oh, you're following me!" he exclaims in that inimitable drawl.
It's all fun and a reminder that, whatever the image the Hollywood machine liked to conjure up, stars were just as prone to error then as now.