Deliberate mistake: When the vortex is summoned to get rid of the monsters, other things get sucked into it. Cars, trees, light poles, other police officers. However other things or people who are more accessible do not get sucked in. For example, Phoebe hiding behind a bench, the bench itself, Phoebe's mother and a few cops hiding behind a cop car, etc.
The Monster Squad (1987)
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Directed by: Fred Dekker
Starring: Stephen Macht, Andre Gower, Duncan Regehr, Robby Kiger
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More mistakes in The Monster Squad
Phoebe: Come on. Don't be chicken shit.
Question: How does the dog get into the tree house?
Chosen answer: Obviously it is carried up there by one of the kids.
Answer: It's unknown how the dog got into the treehouse. After the boys put their hands on top of each others, the dog puts his paw on and Rudy questions how the dog got in with none of the boys being able to give an answer.