Revealing mistake: When John picks his wife up at the airport, it's raining. But look at the people around outside, they are in T-shirts, in the sun, and not getting wet. Obviously the rain is being sprayed on the car.
Continuity mistake: When John, Jenny and Marley are walking on the beach and John asks what's next, they are by some washed up debris. Camera cuts and they are no longer near it. (00:31:00)
Continuity mistake: When John and Sebastian are in their office talking about getting a dog, John takes off his bag twice.
Factual error: When Marley runs on the field during the Marlins' Bark at the Park night, the stadium scoreboard can be seen briefly behind him and John. "WAS" (Washington) is listed as one of the teams playing a game that night, despite the fact that Washington did not have a team before 2004 and the film takes place in the early 90s.
Revealing mistake: When Marley is running away and jumps the fence, John follows and lands on a crashmat disguised as a flowerbed. If you watch closely there is movement in areas John is not by, and this movement is similar to that of a corner of a crash mat going up when someone lands on it.
Continuity mistake: Just before Marley jumps out the car, he has his two front legs outside the window. Camera cuts to a wide shot from the pavement and his front legs are in the car. Back inside the car, his legs are outside again. This is not to be confused with a similar mistake where he is walking with his back legs in/out the car. (00:26:00)
Continuity mistake: In the scene where John takes Jenny to pick out Marley, Jenny has a tie on as a blindfold. When they first get out of the car, the tie ends are hanging long and straight down her back, but when they get on the porch, the knot has changed and is sticking out the side of her head.
Continuity mistake: There is one scene where Jenny and Marley are bonding and Jenny is holding his collar. Camera cuts and now she isn't.
Continuity mistake: In the kitchen, when Jen talks about John's first article in the Sun-Sentinel, John lifts the orange juice container to pour into a glass and its orange lid is on the counter, but next shot the lid is on the container and he has to remove it. (00:07:10)
Continuity mistake: When John says "Whose dog is that?" at the house viewing, the woman in yellow's position changes entirely between shots. (00:55:30)
Continuity mistake: When Jen comes back from her trip and opens the garage door to find puppy Marley and the destruction he caused, the stuffed alligator that Jen holds goes from face up, to tail-end up, between shots. (00:17:10)
Audio problem: When we hear the one kid crying and Jenny gives them to John, you can tell the kid isn't really crying.
Continuity mistake: When John brings Marley home from the breeder and they are driving home, Marley isn't wearing a collar in the car, but suddenly he has a collar on when they pull into the driveway and get out of the car. (00:13:20)
Continuity mistake: When Marley is eating the necklace, the amount of chain hanging out of his mouth changes instantly. (00:37:20)
Continuity mistake: During the scene with John and Marley at the Dog Beach, a woman in a blue bikini walking a miniature pinscher walks by from left to right twice, just before he sits down, and again, from the same spot right after he sits down. (01:52:25)
Continuity mistake: During Marley's poop incident at the dog beach, the wet stain on John's shirt changes repeatedly, from smaller, to much bigger, to smaller, particularly when the guy says, "Dude, that was not cool." (01:17:30)
Continuity mistake: When John and Sebastian step out of the elevator discussing Jen, the spare room, step seven, etc, John's bag strap hangs across his chest with the bag at his right, in the shots facing them once they reach the newsroom, but in shots from behind John's bag hangs straight down on his shoulder with the bag to his left. (00:08:25)
Continuity mistake: When the dog-sitter pulls up in front of the Grogan's house in the exterior shot, the curtains at the window beside the stairs are pulled nearly closed, with only a narrow gap between. Next interior shot, as Marley barks at the window the curtains are pulled more apart, but when Marley pulls Debby outside as the Grogans leave, the curtains are as they were in the first exterior shot. (00:44:10)
Continuity mistake: When John and Sebastian are at the bar by the beach, the people walking by drastically change with every shot.
Continuity mistake: When John is putting the collar on Marley at the dog class, he is having trouble, bent over and wrestling with Marley. The camera cuts to another angle, and he is now standing up, holding the lead and waiting to go. (00:23:00)
