Continuity mistake: When John is at the beach with Marley and first lets him off his leash, John's sweat marks on his t-shirt change from a single line to scattered sweat marks, then back to the single line.
Continuity mistake: When John brings Marley home the first time while Jen's away, the bag of Puppy Chow kibble falls. The bag's position on the floor (note tiles), the amount of kibble and John's hands all change between shots. The fallen kibble also changes between shots as the puppy lies on the floor devouring it. (00:14:10)
Continuity mistake: When John and Jenny are talking about having a kid whilst at the beach, marks in the sand keep changing.
Factual error: As John is dropping his wife off at the airport before picking up Marley, watch the background - a very modern car, possibly a Chrysler 300, is seen driving past, despite the scene taking place in the early nineties.
Continuity mistake: At Obedience School, the breed of dogs changes dramatically between shots. Easiest one to spot is a Husky who keeps disappearing and reappearing.
Continuity mistake: When Marley is escaping from the car he has his legs in the car, then when it cuts to an outside view, they are now out of the car, but Marley's legs are back in the car in the next shot.
