6x20 All the Presidents' Heads

Episode Quotes

Mistakes/Goofs

• Goof (continuity error): When the crew starts licking the Presidents' heads, Dr. Cahill's top under her lab coat changes from purple to white and back again between cuts.

Trivia

• Two separate heads of Grover Cleveland appear in the head museum. This is a nod to Cleveland's two non-consecutive terms as president.
• The act of licking the presidents' heads to invoke time travel parodies the act of "licking the toad." Beginning in the 1970s, a craze began where some people licked toads in order to have a psychedelic or hallucinogenic experience. Bufotenin, a psychoactive toxin found on the skin of some toads, was chiefly responsible for the effect.
• The man with the wide hat and scarf who jumps out of a spaceship and runs into a blue phone booth is a caricature of the Fourth Doctor from Doctor Who (UK) (1963). For almost two seasons, this version of the Doctor traveled with a companion named Leela.
• Opals, central to the time travel in this episode, were once thought to contain mystical temporal qualities.
• According to David X. Cohen, many of the details seen in the crew's visit to the revolutionary era were thoroughly researched and are historically accurate. The Two-thirds dollar bill was a real denomination and modeled after revolutionary currency, the Continental Congress met in New York on the day the crew visits, and the opal that Professor Farnsworth steals from the queen is based on an actual opal found in the Crown Jewels. Cohen admits that one historical inaccuracy intentionally overlooked was Benjamin Franklin's presence in America on that day. In actuality, Franklin would have been crossing the Atlantic Ocean on his way back from Europe.