Revealing mistake: After the Custos's house has been broken into, the next day, the Custos takes a key out of his jacket pocket, unlocks a drawer and takes out a pile of bound papers. When he closes the drawer, he doesn't take the key out of the lock, but he pantomimes his hand returning the key to his pocket.
Revealing mistake: Near the end, where Rosemary is driving the tractor and delivering wet steam to kill the weeds, you can see the vines moving as the camera brushes them aside as it closes in on Rosemary.
Revealing mistake: When the lawnmower man crashes his lawnmower, his right leg has some sort of protection on it; it can be seen by the cut of his pants.
Answer: Regents park.