"Part of him is. He said it was like looking in a mirror, and he was right. But not just the way that he looked. It was... it was his eyes. The pain that was inside them. I've seen that in myself. When I think about how my parents died so violently. Sometimes I want to repay that violence with more violence. I wanna make someone else hurt as much as I do."
"But you don't ever do that. You're not him, you're a good person."
"I know, but it's in there, you know. That's in me. That power, that pain. That's where Savitar comes from. From loss. From losing you.
Barry Allen and Iris West on Savitar
"Cause and Effect" is the twenty-first episode of the third season of The Flash, and the sixty-seventh episode overall. It aired on May 9, 2017.


Barry takes drastic measures to stop Savitar. Meanwhile, H.R. continues to push Tracy Brand to design the trap for Savitar, and Killer Frost returns with an interesting proposal.[src]



Special appearance by

Guest starring




Promotional images



  • Cisco mentions the Star Trek: The Original Series episode "The Enemy Within" in which Captain Kirk is split into good and bad personalities.
    • H.R. mentions having Star Trek: Voyager on his Earth, to which Cisco claims to hate spin-offs. This is likely a tongue-in-cheek joke, considering the fact that The Flash is a spinoff of Arrow.
  • Cisco refers to Barry as "Steel Magnolia", referencing the 1989 film, Steel Magnolias.
  • After losing his memories, Barry asks to be called "Bart", a reference to Bart Allen, who is Barry and Iris' grandson in the comics.
  • Barry is revealed to have been a huge fan of anime in high school, with Iris mentioning that Dragon Ball Z was one of his favorites.
    • Coincidentally, this episode aired on the Japanese-recognized holiday "Goku Day".
  • Rather than "the Flash", Barry suggests that they call him "the Streak", a name which was first used to identify him in the first season of the show.
  • Mick Rory is mentioned at the CCPD as being "off the grid", indicating that the police do not know of his whereabouts. This alludes to Mick currently time-traveling with the Legends.


  • According to Barry's driver's license, it says that he renewed it on March 10, 2014. However, Barry was in a coma from the time of December 11, 2013 to September 2014, so he couldn't have renewed it during this time, assuming that it has to be renewed in person (unless a military member or dependent) like in real-life Missouri that Central City is placed in.
  • Tracy states they require 3.86 terajoules (3,860,000,000,000) of energy to power the Speed Force bazooka, which Cisco claims is more than the energy of the sun. This is vastly inaccurate, as the sun releases 384.6 yottajoules (384,600,000,000,000,000,000,000,000) of energy every second.
    • 3.86 terajoules is also less than the approximate output of a nuclear power plant running at full capacity for two hours.
  • As Savitar's armor begins to attack Barry, Barry's mask is removed. However, shortly prior to the armor stepping on Barry, his mask is seen back on his face.
  • Closeups of Killer Frost's forehead show an obvious line of about 5 mm below her hairline where there is no Killer Frost makeup, as it's not properly blended.


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