Internal BBC memos have revealed how Doctor Who's regenerations were modelled on bad LSD trips.
Documents published for the first time describe how the Doctor's occasional transformations were supposed to convey the "hell and dank horror" of the hallucinogenic drug.
The BBC1 series recently saw the 11th actor take on the lead role when Matt Smith replaced David Tennant.
Regenerations were introduced in 1966 to allow programme bosses to replace the lead actor and write the new face into the show's plot.
In an internal memo dating from that year, producers outlined how the original Doctor, William Hartnell, would be transformed for his successor Patrick Troughton. It also tackled the "horrifying experience" of the regeneration.
"The metaphysical change ... is a horrifying experience - an experience in which he relives some of the most unendurable moments of his long life, including the galactic war.
"It is as if he has had the LSD drug and instead of experiencing the kicks, he has the hell and dank horror which can be its effect," the memo says.
Discussing his appearance, the document says: "His hair is wild and his clothes look rather worse for wear (this is a legacy from the metaphysical change which took place in the Tardis)."
The memos are part of a batch of documents which have been published online today as part of the BBC Archive at bbc.co.uk/archive.