Factual error: When the allies are testing their joke on the private in the field, just before he starts laughing at it, a bright red car drives past behind him. You can see it in a break in the trees. This sketch is set in WW2, and the car is obviously not from that era.
Revealing mistake: The Italian evening class runs from 7 to 8 PM. The clock at the back of the classroom reads 10 to 2.
Continuity mistake: We are told that the Germans develop and broadcast the "V-Joke" in 1944, but when we cut to Terry Jones and Graham Chapman listening to their radio and hearing the joke, the caption reads "1942...Somewhere in England".
Continuity mistake: In the Marriage Counselor sketch, Deidre Pewty is wearing such a tiny miniskirt that when she sits we see she is wearing white knickers. When she undresses behind the screen she throws a pair of black knickers out.
Man's Crisis of Identity in the Latter Half of the Twentieth Century - S1-E5
Continuity mistake: At the start of the interview sketch, and at several times throughout, Cleese says he's interviewing people for a management training course. At the end, however, he suddenly claims it was a job interview.
Oh, You're No Fun Anymore - S1-E7
Continuity mistake: During the science fiction sketch, when Eric Idle is reporting his blancmange sighting to John Cleese the clock in the background jumps backwards a few minutes.
Oh, You're No Fun Anymore - S1-E7
Visible crew/equipment: At the beginning of the 'Camel Spotting' sketch the shadow of the boom mike moves back and forth over Eric Idle.
The Royal Philharmonic Orchestra Goes to the Bathroom - S1-E11
Other mistake: William Knickers' letter, complaining about the sketches, starts "I strongly object ..." but the voiceover says "I object strongly ..."
Plot hole: In the Upper Class Twit of the Year Show, there are five contestants. However, after Oliver runs himself over, in the events that follow there are only four props for the remaining twits (four mannequins, rabbits, and guns); since Oliver's death was unforeseen, shouldn't there be five of each? (This mistake, by the way, is rectified in the film version of this sketch).
Visible crew/equipment: Just after Florence Nightingale gets knocked out, a crew member can be seen behind Michael Palin for a short time.
Suggested correction: The scene is set in an active television studio filming a sinister quiz show. The crew member visible is one of the crew of the fictional television show.
Continuity mistake: At the beginning of the vegetarian restaurant sketch, Eric Idle stands right behind the pointy sculpture. It is quite short and in some shots the points of it are visible right at the bottom of the screen, but in other shots people stand and walk through right where it is meant to be. And in the final shot, when Eric is complaining about the punchline, it is definitely gone.