Basic Trope: A really strange event occurs and is then never mentioned again.
Straight: Alice and Bob are walking, when Bob's dead cat appears out of nowhere and starts meowing in a surreal fashion, and they never mention it again.
Bob's dead cat and three million others come out of nowhere and they start meowing in a grandiose musical number (while rocking out on electric guitars) which ends with their heads exploding, and no witnesses seems to mention it or recollect any memory of it, even though it could be seen for miles.
The entire movie is made of nothing but a stream of bizarre and shocking disconnected events.
Downplayed: Bob's non-dead cat appears and meows strangely, and they never mention it again because it wasn't that weird.
Alice and Bob decided to never mention the dead cat because they didn't understand what happened, so they decided to shrug it off.
Inverted: Bob's life is a constant string of random, unconnected events, and his cat is the only constant theme.
Bob's dead cat comes out of nowhere and starts meowing, and they reference it again, noting on how weird it is.
Alternatively, Bob's dead cat turns out to be a spirit attempting to reveal an important secret, which isn't revealed until near the end.
Alternatively, the dead cat is mentioned in the sequel.
Bob seems to remember his dead cat meowing, but it turns out that it was all a dream and promptly forgets it after waking up.
Bob asks Alice about the time that cat popped out of nowhere. Alice says yes, but they reminisce about a completely different event.
Parodied: Bob and Alice try as hard as they can to act as though nothing happened, even though the cat repeatedly tries to get their attention. It reaches the point where they can hardly hear each other over all the meowing, yet they refuse to acknowledge the cat at all.
Zig Zagged: Bob's cat turns out to be alive, but Bob decides not to mention it because he believes that it wasn't happening, but then he wakes up and it turns out to be a dream, but he remembers the dream completely, and then he comes to the realization that he has no cat, and then he wakes up from his dream to his cat meowing, even though it was supposed to be dead, and then it turns out it was all a hallucination that he doesn't remember, though he vaguely remembers a cat.
Averted: There is no cat.
"So... What's with the cat?" "He's still on contract, just ignore him."
"Guess we don't need this ghost cat subplot in the final film. But let's keep this one scene because the rest of the crew loved it."
Defied: The zombie-cat comes back from the dead and Alice and Bob readopt him.
Discussed: "Is that my dead cat?" "Move on Bob, move on."
Conversed: "...Why the hell is his cat there? It died last season!"
Implied: Bob has a small notepad he uses. One of the visible headings for a page is "unusual items that nobody remembers".
Deconstructed: Bob's dead cat is a sign of his mental illness; because of his deteriorating brain, he believes that his cat died when it actually didn't and his memory suffers as well, not remembering a single detail about anything. His family is worried about him when he creates an imaginary friend, Alice, who also doesn't remember that the cat is alive, and they need to place him inside a mental asylum.
Reconstructed: Bob is looking at old pictures of his beloved cat that died, and the cat's "spirit" seems to be right next to him. He puts the pictures back inside a box and moves on with his life, forgetting the cat but not its influence.
Plotted A Good Waste: There are several character-revealing events that happen like this. They aren't mentioned despite being a glimpse past just the surface of the characters.
Played For Laughs: There is a character who remembers these things like a normal person would, but nobody else has a clue what he's talking about when he brings events up, even if it would make perfect sense for him to do so.