[DanaC]

That's because they do know what the line is before it comes :p Or rather they think they do. Many of these jokes are running jokes. It was recorded in a studio in front of a live audience. Only in the first series of Blackadder did they shoot on location and then play the tape to an audience for the laughter track.


[eta] oftne they're laughing because ofthe build-up to a joke, it's an expectant laugh. Like with Captain Darling and the coffee: that was the 'punchline' to a joke that had taken the first half of the show to build. Or just because they find the expressions of the characters funny. Often they're laughing at stuff going on in the background: the expression on the face of one of the characters who isn't speaking. It's conspiratorial laugher: they're in on the joke in a way that Captain Darling and General Melchiord isnt.