I say it’s pretending to wake up. I’ve rarely seen anyone onscreen convincingly get that somehow non sequitur-ish ‘Huh? What?’ aspect of being roused from a deep slumber. You can sort of tell that they’ve been conscious all along, if you know what I mean.
They also seem to think that it always takes longer to wake up than it really does, particularly in emergency situations. Most people I know can usually snap to in about a second, if they really have to; actors always seem have to be poked and prodded a couple of times.
Give it a try, though. Pretend to wake up. It’s actually more difficult than you might think!
I imagine it is really hard to stop breathing and suppress eyelid twitches, particularly if your “corpse” is being moved or prodded and poked at by the CSI team or whatever. And almost impossible to get the right degree of floppiness of limbs, slack-mouthed gape, etc.
Drunkeness seems to be difficult for a lot of actors to pull off effectively. I think it has to do with the slurring,or lack thereof. Glazed eyes are also a bit hard to fake, I would imagine.
Holding a gun. It’s immediately obvious if the actor/actress has never held a gun before the Armourer put one in their hands and the director yelled “ACTION!”; they tend to hold it awkwardly and uncomfortably, I’ve noticed.
Sneezing. Hearing a fake “ah-CHOO!” totally takes me out of the scene. Hiccupping is another. (One of my few talents is being able to sneeze realistically on demand.)
Any kind of intoxication, really. They almost always overplay it.
A rare scene that does it pretty well is Vince and Mia’s date in Pulp Fiction. Vince is on heroin, and Travolta plays him as low-key and kinda distracted, not as a whacked out of his mind goofball (and he sobers up noticeably as the night goes on). Likewise, Mia is doing coke all night, but she’s just chatty and enthusiastic, not maniacal.
You can also usually tell which actors don’t smoke; they pay too much attention to the cigarette and it looks unnatural.
True, unless you happen to be the very wonderful and very funny Foster Brooks.
Another mundane task that never looks right is driving, in any scene involving back projection or equivalent. It seems that with all the advances in movie-making, there’s still no way to get it to look even half-way convincing. Maybe there’s no need.
It’s obvious (to me) when someone breathes in, and then exhales, a lung-full of smoke, it’s equally obvious when someone just takes a mouth-full and puffs it back out.
I think that generally acting surprised when you in fact exactly know what’s coming is hard to do, and separates the genuine actors from the day time soap ‘stars’.