When the unsub has his first flash back, he hits the mirror next to him twice, destroying the bottom part, but when the camera moves, the bottom part of the mirror is still intact.
When the unsub is assembling one of his bombs that are hidden inside a book, he fills the hole where the bomb sits with items such as screws, however a couple of the screws don't land inside the hole and instead on the edges surrounding the hole. He then proceeds to put the stray screws back into the hole but mistakenly leaves one stray screw on the edge surrounding the hole as he closes the book.
When Fred and Laura explain how they knew other victims' relatives, they tell how they rented a car with them in Montreal and drove around the countryside. But when Emily and Luke are examining the route they took with the car, the map shows they only drove on the two main islands of Montreal, never venturing out of the city.