Revealing mistake: When Damian knocks Lee Remick over the balcony with his tricycle, five big goldfish in a bowl get knocked over, too. But the fish don't move; they don't flap around like fish do out of water. They are obviously fake fish.
Revealing mistake: In the second murder, the killer of the first one is bashed in the head by a monkey wrench, her head split open. A second hit ensues, but there's no reaction to it, no further spraying or damage, the head itself barely moves, and with delay. (00:04:30)