It is obvious that Patrick McNee doesn't perform the stunts. His double is very recognizable.
Henry Averman tipped a dozen or so of his pills into his pillbox. They were bright pink.
Bristow's manservant took the pillbox and abducted Averman.
When the stock market game started the pills were shown to be in the graph. They were now bright red instead of pink and there were hundreds of them.
Henry Averman's telephones are constantly ringing with calls from around the world (he is a stockbroker) yet when the fight starts between Steed and Bristow's manservant, the telephones are suddenly silent.
During the Stock Market game, the close up of Averman as he says "Take an option and hold" was added later as the actors make up is different: there is no perspiration on his face which there is before and after the close up shot.
When Steed gives Tara the jigsaw pieces from Cooty Gibson, he says "Check them for me, at Jig Creations". This line was added in post production because the sound quality is quite different.
As the Brigadier's Jeep crashes, the tree topples backwards revealing that it has been sawn through.
During the fight at Henry Averman's house, Garfield Morgan's stunt double can be seen, wearing a badly fitted bald wig.
Bristow's manservant fired a toy dart into Steed's apartment in order to inform Steed of Averman's whereabouts.
This should not have been possible though, because the window was closed and covered by a net curtain.
Steed told Tara that Clive Dexter died of a snake bite. The snake was a toy. What really killed Dexter was a fall from an exceptionally high ladder.
The Brigadier had no idea that Steed and Tara would drop into his trench yet when his man brought the tea tray, it was set for three people.