David considers whether the voices he hears might be real .
A montage of David Haller's life is shown, starting from infancy and ending right as he attempts to hang himself as a young adult. As a result of this suicide attempt, David is admitted to Clockworks Psychiatric Hospital. On his birthday, David's sister Amy visits and asks him about how he is doing, but David
- Dan Stevens as David Haller
- Rachel Keller as Sydney Barrett
- Aubrey Plaza as Lenny Busker/Farouk
- Bill Irwin as Cary Loudermilk (credit only)
- Jeremie Harris as Ptonomy Wallace
- Amber Midthunder as Kerry Loudermilk
- Katie Aselton as Amy Haller
- Jean Smart as Melanie Bird
- David Ferry as Dr. Kissinger
- Ellie Araiza as Philly
- Matt Hamilton as Ben
- Brad Mann as Rudy
- Quinton Boisclair as Devil With The Yellow Eyes
- Mackenzie Gray as The Eye
- Mike Azevado as 'Renal Failure' Alvarez
- Ese Atawo as Day Room Duty Nurse
- Tobias Austen and Noah Hegglin Houben as David (Infant)
- Sebastian Billingsley-Rodriguez as David (Toddler)
- Christian Convery as David (4 yrs)
- Luke Roessler as David (6-8 yrs)
- Jacob Hoppenbrouwer as David (10-12 yrs)
- Alex Mulgrew as David (16 yrs)
- Paul Belsito as The Man Who Hides
- Eugene Wong as The Man In All His Clothes
- Eric Malapad as The Man Who Strokes His Beard
- Gustavo Ferman as Risotto Dude
- Stephanie Van Dyck as Skeletal Fat Lady
- Tim Bissett as Psychiatrist
- Sidartha Murjani as Wild Rusty Combo
- Georgia Swinton as Woman Who Self-Argues
- Espirito Muricio as Woman Who Nurses
- Kyja Sutton as Amy (8-10 yrs)
- Matthew Afonso as Monitor Room Technician
- Peter Chao as Cube Tech #1
- Jesse Reid as Cube Tech #2
- Simon Chin as Clockworks Orderly
- Charles Jarman as Cube Police #1
- Shimon Boriskov as Jr. Prom Guy (Bloody Nose)
- June B. Wilde as Science Teacher
- James Wilson as School Principal
- Maddie Phillips as Jr. Prom Date (Crying)
- Mathias Ty Parto as Trick or Treat #1
- Jonathan Wu as Trick or Treat #2
- Belinda Sobie as Patient Dancer #1
- Sabine Uwimambe as Patient Dancer #2
- Karina Ho as Patient Dancer #3
- Edwin Perez as Patient Dancer #4
- Mandy Rushton as Patient Dancer #5
- Monica Gutierrez as Patient Dancer #6
- Stephanie Lavigne as Patient Dancer #7
- The Devil With The Yellow Eyes appears as one of David's toys in the opening montage.
- Several characters refer to an "incident at Red Hook." Red Hook is the name of the town next to Bard College, where Marvel character Jean Grey was buried. Jean Grey's father was a professor at Bard College and Jean Grey grew up in the area.
- To depict David Haller losing control of his abilities in a kitchen, actor Dan Stevens was filmed separately from the practical effects, with the images layered together to create the final, slow-motion sequence.
- During the episode there are various people that only David can see, such as: the old couple when talking to his sister, and the man in the greenery when he's sitting with Lenny. These are not actually delusions and are, in fact, some of David's personalities.
- When Syd and David switch bodies, she is able to tap into the powers on one of his personalities. Known as Personality #5 in the comics, Personality #5 is a godlike mutant who describes himself as "The One True Legion". He has the ability to warp both time and reality which would explain how Syd was able to change the structure of the patients rooms, leaving no doors, as well as, trapping Lenny in the wall.
- David is seen in a wheelchair early on in the episode in the hospital. This is a reference to his father in the comics, Professor Xavier.