I find it sort of strange and sort of interesting that some events take place in stories because they took place in previous stories and have become sort of weird convention. It's even stranger when these events don't happen naturally in real life. For instance, I've lost count of the number of times someone on TV has magnified a grainy photograph a few hundred times and then 'enhanced' it to reveal an important clue. That might have worked before most of us had either digital cameras or much experience of computers, but surely no one is fooled now. We don't really think that even the most powerful computer can take the three dots on a photo that represent a shiny brass button and reveal a reflection which shows the number plate of the killer's car, do we?

Likewise I've mentioned before my surprise at how often I see a 'binary explosive' on TV. Nothing wrong with the idea of a two-part explosive, any more than there's anything wrong with the idea of a two-part glue, but in movies it's always used as a way to evade detection because the two components are harmless before you mix them. We've all seen it half a dozen times on TV and are probably quite surprised to find it's make believe (which is a problem if you happen to be locked up for planning to make such a thing).

Strangest of all is the Hollywood view that if you show people in a spacecraft floating weightlessly it won't look real, so they're shown in a sort of slow-motion instead which the audience interprets as weightlessness and supposedly finds more convincing. In case I didn't make that clear, I'm saying that real weightlessness is thought to look fake, so Hollywood has invented its own fake weightlessness which apparently looks more real. Check out video footage from shuttle missions if you want to see what I mean; it looks nothing like 2001.

I've even seen B movies with time travel devices in them which feature a little three-pronged dealie-bob like the flux capacitor out of Back to the Future. Of course that could just be an homage, but I doubt it. The last thing most B movies want to do is raise the suspicion that they're lifting their ideas from popular blockbusters - specifically popular blockbusters with enough money to afford scary intellectual property lawyers. No, sad to say, I think it's much more likely that whoever designed these knock-off flux capacitors thinks "that's how time machines look".

Of course lots of weird and unrealistic things that happen over and over in movies happen simply because they're awfully damn handy if you've got a plot to service. And there's a sort of pleasurable frisson of recognition when you have one pointed out to you. For instance, it is an inviolable law that if anyone in America is murdered, their front door unlocks itself making it easy for the next visitor to discover the body.

If you haven't already read it, Roger Ebert (who's America's Barry Norman) has compiled a highly entertaining collection of them in The Bigger Little Book of Hollywood Cliches and I recommend it.