Ouroboros is a symbol of a snake (sometimes dragon) eating its own tail in a circle, and often symbolizes eternal recurrence (something coming back in a similar form infinitely), something recreating itself constantly, or a phoenix-like cycle. It can also symbolize eternity, or something so great it cannot be extinguished and endures forever.
The performer who played "Crabby Joe" was buried up to his waist in sand. To protect him from being pinched, the ghost crabs were added digitally.
To create the effect of the gruesome spinal injury on the plane passenger, they used practical effects makeup. A harness was fitted with a spine made of urethane - a synthetic crystalline compound - and covered in fake blood.
Rubén Blades, who plays Daniel Salazar, says that Frank Dillane is the best of the cast at driving the Zodiac.
As this episode takes place in a timeline before the first season of The Walking Dead (2010), this means that this is the first time a character discovers that, if they are smeared in zombie guts, they become invisible to the walker horde. This happens to Nick in this episode and is a tactic that Rick Grimes uses several times in the main show.