Cause and XS

"The ripples you'll cause, whose life you're gonna affect. No one can do that."

"No one?"
"No. We're not gods, Nora. We've just been given extraordinary abilities."

—Barry Allen and Nora West-Allen

"Cause and XS"
Information
Season 5 » Episode 14
Episode number	106 of 184
Original airdate	February 12, 2019
Written by	Todd Helbing Jeff Hersh
Directed by	Rachel Talalay
Guest stars
Victoria Park as Kamilla Hwang
Chronology
Preceded by	"Goldfaced"
Followed by	"King Shark vs. Gorilla Grodd"

"Cause and XS" is the fourteenth episode of the fifth season of The Flash, and the one-hundred-sixth episode overall. It aired on February 12, 2019.

Synopsis

After Iris lands in serious danger, Nora races to save her mother. Barry puts the finishing touches on the meta-human cure, leaving Cisco with a rare night off so he decides to take Kamilla Hwang on a date.

Trivia

• The episode's title is a play on the phrase "cause and effect". Coincidentally, that very phrase was the name of an episode in season 3.
• This is the first episode of The Flash in which Grant Gustin doesn't have a lead role.
• Nora resets the timeline 52 times (53 if the time where no one gets killed is counted), a reference to the famous DC number 52.
• Cisco states that giving the cure to Cicada in a month would be very fast for them to stop a big-bad. This is a fourth-wall reference to the fact that it's always taken a full season for Team Flash to defeat each main antagonist.
• Barry teaches Nora about time travel, using the example of a coffee cup being like the space-time continuum, breaking whenever you travel through time, directly quoting what Jay Garrick had told him about the consequences of time travel in "Paradox"​. 
• The animation when Nora runs back in time is somewhat similar to the animation of Earth-90's Barry Allen when he time traveled in his version of The Flash​​​.
• Cisco mentions Sun Tzu to Ralph Dibny, who is a Chinese general, military strategist, writer and philosopher who lived in the Eastern Zhou period of ancient China.
• The events of this episode are very similar to the events of the DC's Legends of Tomorrow​​​ episode "Here I Go Again"​​, in which Zari Tomaz is stuck in a simulation of a time loop, reliving the same hour over and over again with the Waverider exploding at the end of each loop. Here, Nora ends up being able to run only one hour into the past to keep anybody on Team Flash from getting killed by Cicada.
  • In addition, in "Here I Go Again", before Zari realizes she's stuck in a time loop, she feels as if she's experiencing déjà vu. In this episode, due to the fact that his powers allow him to remember things that have happened to him in erased timelines, Cisco gets the feeling that he's having déjà vu.
  • Furthermore, in "King Shark vs. Gorilla Grodd", the next episode, Joe describes what happened here (with Cicada kidnapping different members of Team Flash, where someone always gets killed) as a time loop.
• The first time that Cisco goes on his date with Kamilla (before Nora resets the timeline for the first time), he says that the company he works for is called Ramon Industries, a reference to the company he owned in the Flashpoint timeline.
• It's revealed that Kid Flash and Cicada both have drinks served at CC Jitters named after them.
  • However, a deleted scene from the season 3 episode "Duet" had also featured the Kid Flash drink from CC Jitters.
  • In all of the instances where Cisco goes on his date with Kamilla, a man named Ian orders a Cicada, but in the last iteration of the timeline (where none of Team Flash gets killed), a man named Stephan is there instead, who orders a Kid Flash. Moreover, the barista mispronounces both of their names, only to be corrected by the customer.