Revealing mistake: When Jerzei is coming through the door with an axe, you can see the door is paper thin to make it easier to get through. In fact you can see Alexei Sayle being very careful to only chip small bits away because a decent whack with the axe would smash the whole thing down.
Visible crew/equipment: When the landlord is about to start smashing holes in the door, a boom mic creeps into the top of the screen.
Answer: Madness also appeared in the episode "Sick", where they performed their song "Our House", which was their biggest (and only major) hit in the US.
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