Turner Classic Movies was showing Frankenstein movies on Halloween, so I TiVoed the original, “Frankenstein” (1931), and watched it today. It’s one of those essentials of film history that I’d never seen before, so I figured I ought to, if only to help me deal with people who assume that because I’m a movie critic, that means I’ve seen every film ever made. (“You’ve never seen [name of movie]?!” they say, astonished that it is possible for a man of the world not to have seen whatever title they’ve pulled out of their butt.)

I’m fascinated by how society’s tastes change over time. Simply put, people were more easily amused in the old days, more easily scared, more easily entertained in general. There weren’t as many media vying for their attention. They had radio, movies, books and magazines, and not nearly as many of those things as there are now. Then of course TV came along and changed everything, and then video games and the Internet changed it some more, and now people are much harder to entertain because they’ve seen so much already.

I mention this because “Frankenstein” is not the least bit frightening, hardly even atmospheric, and only barely competent in the way it’s assembled. The editing is shoddy, the sets are cheap, the “monster” is a guy in admittedly pretty good makeup clunking around in huge platform shoes.

But in 1931, it had people wetting their pants, probably literally. Dr. Frankenstein’s line “Now I know how it feels to BE God!” caused outrage and was removed (it’s been restored now), and the moment when the monster throws the little girl in the lake was taken out, too (also restored now). Today, neither of these elements would make anyone bat an eye.

I will say this for it, though: It lets a kid die. I’m always frustrated when films about killers refuse to let them kill children. Even the “Friday the 13th” series — a group of films known for their cruelty and for killing people of all types — adhered to this rule. Teens were OK; young children were not. “Frankenstein” let the monster toss a girl in the water because he thought she would float like a flower. She drowned. Whoops! Good for “Frankenstein.”

(A year before “Frankenstein” came out, Germany produced its first major talking picture, “M,” about a serial child murderer. “Frankenstein” takes place in Germany, too. Perhaps the rule is that only German children are allowed to be killed in movies. Fine with me. It’s a start.)

Even if you haven’t seen “Frankenstein,” you probably know the basics, through references or parodies you’ve seen. The doctor yelling, “It’s alive!,” the monster grunting pretty much the way Phil Hartman used to do in his “Saturday Night Live” impersonations, the mob of angry townspeople carrying torches as they pursue the creature — they’re all there.

There’s no Igor, though. Frankenstein has a wormy, hunchbacked assistant, but his name is Fritz. And the mad doctor doesn’t work out of a castle, but out of an old windmill, don’t ask me why.

The film is 71 minutes long, not at all uncommon for movies before 1950. One curiosity about public taste is that even though people’s attention spans have gotten shorter over the years, movies have actually gotten longer. Sixty minutes is considered the length for something to be a “feature film,” and quite a few of them back then barely reached that point. Now, very, very few major releases are shorter than 80 minutes, and those are almost always animated films.

I suspect the reason for longer movies now is mostly financial. Film — the actual stuff the movies are shot on — costs money, and movie producers are richer now. Since the 1970s, we’ve also placed a greater emphasis on directors (who were mostly personas not grata, with a few notable exceptions, before that), and directors like to shoot stuff. When the studios ran things, as in the 1930s and ’40s, they wanted to save money, not spend it, and this resulted in shorter products. Once directors were given more control, you started seeing the huge, bloated, over-long films we often encounter today.

By the way, the director of “Frankenstein” was James Whale, portrayed by Sir Ian McKellen in the 1998 film “Gods and Monsters” … another movie I haven’t seen. Give me some time.