What is the LCD "twinkling" effect?

[LukeAP]

I see a lot of reviews talking about "twinkling" during video playback on LCD screens, what exactly is this effect and how do you spot it?

What people describe simply sounds like MPEG artifacting noise, but why should an LCD make that any worse?

I am quite technically minded, so if someone can describe what causes it that would be useful.

Thanks,

Luke