When coughing occurs in a movie, we know that movie cancer will happen.
When a woman spontaneously throws up (not as part of a hangover), she’s pregnant.
When blood comes out of your nose, you’re dead.
Also, when a woman faints or cradles her stomach.
Phone calls in the middle of the night are never good.
When a young couple in a horror movie has sex, we know that they’re about to die.
When someone gets shot in the shoulder, we know that they’ll live. When someone gets shot in the stomach (particularly in a Western), we know that they’ll die.
That’s the one I wanted to say. But as an addition, she will be the last one to know. As a corollary, if she realizes that it means she is pregnant, she really isn’t.
Back on topic: If you are badly wounded, and you lose consciousness, everyone immediately just assumes that you are now dead. There is crying and sadness by the person cradling your head, but no checking for vital signs.
When the creepy music starts in a movie, we know the shark will bite.
When it doesn’t put the lotion on its skin, it gets the hose again.
A podcast I listen to was just talking about something similar -
Knives are deadlier than guns. Someone can get shot multiple times in a movie (usually a western) and live long enough for some final words or survive altogether, but if they get stabbed-- INSTANT DEATH.
If a woman is pregnant when the movie begins, she’ll give birth by the end (exception: Fargo).
Chekhov’s Fetus. 
When the phone rings in the police chief’s or city editor’s office, he (and it’s **always **a “he”) will pick it up, say his last name (usually something like “Murphy!”), and go "WHAT?!?"
When the lowlife the hard-nosed gumshoe’s been trailing all evening gives him the slip, the dick will barge into the lobby of his seedy hotel and ask the night clerk “Where’s Murphy?” And the night clerk (usually a Percy Helton–type) will say “Oh, Mr Murphy? He just went up the stairs!”
When there is a secluded cabin in a movie, we know a murder will occur.
Cop’s/soldier’s partner/buddy starts talking longingly of seeing his loved ones, he’s going to die in the next scene.
When the jilted lover decides to run to his girlfriend’s house to see her, there will be an immediate downpour. Even if it’s in a desert or her place is in the same building, 'cause nothing says “I love you” like being soaking wet.
Hero falling off a cliff, minor damage. Bad guy falling ten feet into water, instant death.
On Combat!, it was always the replacement who was finally gonna sit down and write that letter home he’d been putting off.
When there is a woman and a man in a Lifetime movie, she is virtuous and he is villainous.
When there are two women in a Lifetime movie, one is the heroine and the other is the villain.
When there are two women and one man in a Lifetime movie, he is useless.
When the star is a strong, intelligent, woman professional, every man with whom she has contact will be a hopeless idiot, save one. And he will be the one she falls in love with.
When the actor wears a red shirt on Star Trek, he’s gonna die, to move the plot along.
If you can’t find the body, he’s not dead.
When a when someone is riding a bicycle in a scene, you will always hear the stereotypical “ching-ching” sound.
When there is a scene in an office cubicle farm or in a hospital wing, you will always hear a phone ringing (modern ring) and see miscellaneous people milling around in the background.
When there is a scene at a crime location, it is always introduced with the “woo-woop” siren sound.
When more than peripheral attention concentrates on a dog in dark/Disney flicks, the dog is gonna die.
When a dog is off her feed, she’s on the way out (see: Isis of Downton Abbey).