Revealing mistake: When Tim Curry runs out of Kevin's hotel room after being scared by the inflatable clown doll he hits his knee on a table. When he hits the table and then hops away you can clearly see that he is wearing a knee-pad.
Revealing mistake: When Kevin arrives at the airport in New York and goes up to the agent to ask her what city is outside the window, one of the destinations on the board at the gate is New York - LaGuardia, giving away that the scene was not filmed at a NYC area airport (because flights don't go from one New York airport to another). The scene was filmed at Chicago O'Hare.
Revealing mistake: In the scene when the bandits are in the uncle's house at the bottom of the stairs, the tool chest falls down. When it hits the door and they slide back if you look closely you can see that they are on rollerblades.
Revealing mistake: Makeup is visible before the first brick hits Marv Merchants.
Revealing mistake: When Kevin breaks the pearl necklace while being chased by Harry and Marv, the hands doing the breaking are not Kevin's, they are much too big to be his.
Revealing mistake: In the scene at the end when Marv and Harry are talking to Kevin on the roof, if you watch it when Kevin throws the brick down at them, the one brick hits Marv. They cut film somehow so you wouldn't notice easily, but when it hits Marv you can see the corner buckle in, as it's a sponge made to look like a brick.
Revealing mistake: In the whole scene where Harry's head is caught on fire to the part where it shows the explosion outside the building, this is quite obvious that the whole scene was done during the day.
Revealing mistake: In the scene where Kevin runs into his relative's abandoned house in the middle of the night to set the traps, he runs down a ramp. You can tell that shot was filmed in broad daylight.
Revealing mistake: When Harry and Marv are standing at the crossing with Kevin, they have a firm grip on him. But if you look carefully, before Kevin reaches forward to pinch the lady in front of them, Harry slightly loosens his grip on Kevin so that Kevin has enough leeway to lean forward to pinch the lady.
Revealing mistake: This film takes place around Christmas, however, when the airport shuttle vans leave the McAllister house to head for the airport, there are short shadows under the vehicles, indicating it was filmed during the summer.
Revealing mistake: Just after Mrs. McCallister screamed "KEVIIIN!" as she realised his son is lost again and faints, there's a little girl in the background who looks at her falling backwards and then at the camera for one second.
Answer: I think they are just more shocked with how brazen Kevin is with telling off his uncle.
Phaneron ★