Visible crew/equipment: In the kitchen scene with Basil, Sybil and chef, Basil says, "Would you believe it, I give him his breakfast, I take it all the way upstairs." At this point, the shadow of a boom microphone on the wall to the right is visible.
Revealing mistake: Just after Polly comes down to to the kitchen to tell Sybil that Mr Leeman's dead and they leave, Basil wanders back in, to learn the news. Watch the wall on the right on the staircase when Basil shoves past Sybil on the stairs. The wall shakes so much at that point it's virtually impossible to miss.
Add timeNeil Jones
Revealing mistake: When Basil, Manuel and Polly are trying to hide Mr. Leeman from the other guests, they put him in a cupboard. While they are talking to the people staying in the room, Mr. Leeman's hand comes out of the cupboard. Watch carefully, and you can see the actor opening the door from the inside, and then putting his arm down, making him look like the corpse.
Character mistake: When Sybil is telling Basil that the two men and the woman are coming to collect Mr Leeman but he's already pronounced dead, she tells her husband that they are coming to collect him "at lunchtime". However, his colleagues told Mr Leeman they'd collect him at 9:30 and not lunchtime.
Visible crew/equipment: When Basil, Manuel and Sybil enter the office and find Miss Tibbs fainted next to the corpse, the boom mic appears on the righthand side of the screen next to the fan on the wall. And when the camera switches back to the full shot of all the characters, the boom mic appears again.