1. The actress who plays Yoga Jones was the voice of Patty Mayonnaise on Doug.
2. Pablo Schreiber, who plays "Pornstache” Mendez, is Liev Schrieber's half-brother in real life.
3. Laverne Cox's (Sophia) real-life twin brother played her pre-transition in the flashback sequence in Episode 3...
4. ...which was directed by Jodie Foster.
5. Yael Stone, who plays Morello, is Australian.
6. This is Crazy Eyes in real life (actress Uzo Aduba).
7. The bartender from Episode 7 is actress Lindsay Felton, who played Caitlin in Nickelodeon's Caitlin's Way.
8. This is the real Piper and Larry...
11. There is an American Pie reference in the first episode of the series.
12. Red is actress Kate Mulgrew. You may may know her as Captain Kathryn Janeway from Star Trek...
13. ...and there was a Star Trek reference between her and Nicky where she didn't know who Spock was.
14. The opening-credits music was written and performed for the show by Regina Spektor.
15. This guy from Episode 12 looks like Leonardo DiCaprio:
16. The scar we see on Nicky is a real scar from heart surgery Natasha Lyonne had in 2012.
17. Jason Biggs' character was watching Weeds in one episode, which was created by this show's creator Jenji Kohan...
18. ...and Natasha Lyonne, Pablo Schreiber and Michael Harney all made appearances on Weeds.
19. Actress Taryn Manning, who plays Pennsatucky, is cousins with Eli and Peyton Manning...
...and was in the 2002 movie Crossroads.
20. Laura Prepon and Lauren Lapkus were costars on NBC's Are You There, Chelsea?
21. Taylor Schilling, who plays Piper, looks like Jared Leto.
(It's a fact!)
22. Matt McGorry, who plays CO Bennet, used to be a body builder and personal trainer.
You can see plenty more of him here.