Cisco has finished the metahuman cure, but it turns out it has to synthesize for a month before it can be used. Barry takes it into the Speed Force for an hour to speed up the process. But while he's gone, Cicada kidnaps Iris for a trap, Killer Frost is injured, and Nora wants to use her powers to help avert catastrophe, but the results aren't what she expects.
- An Aesop: Don't try to fix everything by yourself, your friends and teammates are there to support and help you.
- Arc Number: Nora tried to change time 52 times before finally getting things right.
- Bad Date: Cisco's date with Kamilla, 52 times. Until he starts acting naturally.
- Be Yourself: Again, it's what Cisco needed to do to make that date go well.
- Brutal Honesty: Ralph telling Cisco that, based on his research, the latter is not Kamilla's type.
- The Bus Came Back:
- Cecile returns after being absent for a few episodes.
- Kamilla Hwang, the bartender with whom Cisco exchanged numbers, goes on a date with him (or multiple ones, due to Nora's time travel shenanigans).
- Call-Back: Barry gives Nora the same lecture that Jay gave him about time travel, including the coffee cup analogy.
- Didn't Think This Through: Iris' extremely reckless idea of going to Cicada's house last episode comes to haunt her as it DOESN'T take much effort on Orlin's part to track her down and realize her connection to the Flash.
- "Eureka!" Moment: Nora realizes she can use her journal entries and the team's expertise to plan how exactly to defeat Cicada.
- Sherloque realizes that with the team's help Nora can reverse time so Cicada's dagger will hit him instead.
- History Repeats: Just like her dad before her, Nora has to learn the painful lesson that a speedster's time travel abilities are not to be used cavalierly.
- Idiot Ball: Despite knowing that Cicada can nullify meta powers, Ralph doesn't instantly go on alert when his powers suddenly stop working while he's in his office.
- In Spite of a Nail: No matter what Nora does, Cicada goes after somebody from Team Flash who's by themselves outside of S.T.A.R. Labs and somebody is stabbed by Cicada's dagger in the rescue attempt. First it's Iris in her office, then Ralph in his office, Sherloque breaking into Iris' office, then Cecile, and then 48 attempts with some variations of the above.
- In the Back: How Cicada keeps killing Nora's friend throughout her 52 tries.
- Ironic Echo: "Told ya."
- Leaning on the Fourth Wall: When everybody is shocked about the cure still taking 1 whole month until it is ready to be used against Cicada, Cisco lampshades the fact that this would still mean they'd defeat him one month earlier than all previous Big Bad's.
- Locked Out of the Loop: Expected given the circumstances, but Barry was rather taken aback to learn that not only Cicada was targeting the others, but that Nora time traveled 53 times within an hour.
- Lured into a Trap: Cicada kidnaps Iris as bait for Killer Frost and XS. In the other timelines he goes after Ralph then Sherloque, then Cecile. In the end they use the fact that he's actively seeking them out to lure him into their trap.
- Mundane Utility: Ralph's attempt to stretch out his hand to grab a bottle of beer at the other end of his office is what tips Cicada off that there's a meta in the office next to Iris'.
- My Greatest Failure: Nora sees her inability to stop Cicada from killing a member of Team Flash in 52 timelines as this.
- Poor Communication Kills: Nora doesn't tell anyone the truth of what's actually happening, leading to the seemingly endless cycle of Cicada successfully killing at least one member of Team Flash. When they themselves finally deduce what's going on and Nora comes clean, they are able to work together to come up with a plan that successfully hurts Cicada (thus scaring him off) without anyone dying.
- Pronouncing My Name for You: Two customers tell the clerk lady their preferred annunciation for their names: "Eye-an" not "EE-an" and "Stef-AHn" not "Stef-ehn".
- Properly Paranoid: Nora is worried what will happen if Barry is gone for an hour. Her fears turn correct when Cicada comes out of hiding to target Team Flash.
- Ripple-Effect-Proof Memory: Cisco vibes every outcome of his date with Kamilla after every time Nora travels through time again.
- Screw Destiny: What seems like a fixed point in time, turns out not to be so when Nora stops trying to carry the weight of the world on her shoulders and lets her teammates help her.
- Screw This, I'm Out of Here!: When Ralph brings "The Book of Ralph" everyone sans Nora and Cisco vamooses out of there.
- Set Right What Once Went Wrong: Nora thinks she can evoke this to stop her teammates from getting hurt, but like her dad and the Legends have learned before her, time travel just doesn't work that way... at least until she fills her teammates inNora: [in tears] Why can't I fix this?!
- Shout-Out:
- The title is a reference to "Cause and Effect", the infamous "Groundhog Day" Loop episode of Star Trek: The Next Generation.
- Cisco and Nora mention the movie Breakin and its sequel Breakin' 2: Electric Boogaloo.
- Spotting the Thread: Team Flash is able to deduce Nora's been rewriting time thanks to Cisco's vibes, and her general distraught behavior.
- Stalker without a Crush: Cicada manages to track Iris to her home, having found the connection between her and Team Flash.
- Suddenly Shouting: When Nora asks Thawne if he knows what he's doing, he screams the reply at her.Eobard Thawne: I'm the only speedster who knows what he's doing!
- Wham Shot: Sherloque apparently manages to decipher Nora's journal, likely helped by Nora being forced to explain her records — written in the coded language — of the repeated hour.
- What the Hell, Hero?: It's extremely mild, but given that Nora tried to change time 52 times — well 53, Barry lays down the ground rules, telling her that she got very lucky there are (as far as he knows) no ill side effects from her attempts and she should use her powers more carefully in the future. As the viewers see during the Wham Shot, Nora's timeline tampering gave Sherloque a breakthrough he otherwise wouldn't have had.
- Year Inside, Hour Outside: More so than usual considering Nora's time travel escapades, Barry spends an hour in the Speed Force, but winds up missing 53 timeline alterations.
- You Are Better Than You Think You Are: Cisco manages to get Nora to succeed in stopping Cicada killing one of their friends by encouraging her to be herself - just as he does with Kamilla this time.
- You Have GOT to Be Kidding Me!: When Nora is getting Barry caught up to speed on what he missed:Barry: (taken aback) 52 times?Nora: (awkwardly) 53, if you include now.
