History Trivia / HappyDeathDay

* DawsonCasting: The two leads were way past college age, with Creator/JessicaRothe already 30, and Creator/RubyModine 27.

** In the original ending, [[spoiler: Stephanie Butler [[FaceHeelTurn turned heel]] and killed Tree at a hospital, doing so in an act of revenge.]] [[CruelTwistEnding Being such a downer]], test audiences hated it.

* BannedInChina: Not the movie itself, but the shot of Tree's nude backside when she goes streaking.
* DawsonCasting: The two leads were way past college age, with Jessica Rothe already 30, and Ruby Modine 27.

* ThrowItIn: Jessica Rothe improvised a few of her lines, most notably "Who takes their first date to Subway? It's not like you have a foot-long."

** The killer originally wore a pig mask, most likely changed to deviate from Blumhouse's ''The Purge''s sequels that also depict serial killers dressed like pigs.

** The killer originally wore a pig mask.

** In the original ending, [[spoiler: Stephanie Butler [[FaceHeelTurn turned heel]] and killed Tree at a hospital, doing so in an act of revenge.]]

* HarsherInHindsight: The circumstances portrayed in the film (i.e. a college co-ed attempts to murder her classmate or room mate over something petty and often as not succeeds in doing so) happens in RealLife more often than one would like to think. It's nowhere near as funny and no, there are no cosmic do-overs for the victim.

* HarsherInHindsight: The circumstances portrayed in the film (i.e. a college co-ed attempts to murder her classmate or room mate over something petty and often as not succeeds in doing so) happen in RealLife more often than one would like to think. It's nowhere near as funny and no, there are no cosmic do-overs for the victim.

* HarsherInHindsight: The circumstances portrayed in the film (i.e. a college co-ed attempts to murder her classmate or room mate over something petty and often as not succeeds in doing so) happen in RealLife more often than one would like to think. It's nowhere near as funny and no, there's no do-overs for the victim.

* HarsherInHindsight: The circumstances portrayed in the film (i.e. a college co-ed attempts to...and often as not succeeds...murder her classmate or room mate over something petty) happen in RealLife more often than one would like to think. It's nowhere near as funny and no, there's no do-overs for the victim.

* SerendipityWritesThePlot: Tree and Carter watch the news in the diner because the filming permit in the campus was over, and so they had to shoot it in the other location.

* IKnewIt: Some viewers of the trailers guessed that [[spoiler:Lori is the killer]], because [[spoiler:the candle she drops to ignite the gasoline is the same one from the cupcake she gave Tree earlier]], which is shown in the trailers.

* FocusGroupEnding: [[https://www.cinemablend.com/news/1714429/happy-death-day-shot-an-original-ending-that-made-test-audiences-furious In test screenings]], the ending had [[spoiler:Tree murdered again]]. [[CruelTwistEnding For]] [[YankTheDogsChain obvious]] [[ShootTheShaggyDog reasons]], test audiences hated it, so the director decided to just put the happier one that's in the final cut.

* WorkingTitle: "Half To Death".

* TrailersAlwaysLie: The trailer shows a shot of the "Save the world" girl Tree sees everytime she goes outside Carter's building while she and Carter are talking about possible suspects. In the movie proper, she never serves as anything other than light comedy relief, isn't a suspect, and doesn't even get a name.