Deliberate mistake: At Natalie's house, when she is leaving and Lenny is taking a picture of her, the background looks totally different than from what is shown on the picture: the curtains are opened wider, the door is half open, there is a lamp on the left and there is no mirror on the wall.
Deliberate mistake: When Natalie writes the 'Dodd' note at her home, it just reads, "Dodd, MonteRest Inn on 5th St., room 6, put him onto Teddy..." However when Leonard reads the note in the car and at the motel, the note now reads, "Dodd, white guy, 6'2", blonde, MonteRest Inn on 5th St..."
Deliberate mistake: At the start of the film, when it's shown in reverse that Teddy lifts his head off the floor and his glasses rise up towards his face, in this particular shot it is very apparent that it is NOT Joe Pantoliano, who plays Teddy, that lifts his head off the tile.
Deliberate mistake: The license plate on Teddy's car is constantly changing. When Leonard reads his card of the plate number, it could end either with 7IU or 71U since his I's and his 1's are written in the same way. When Natalie gives him the information, the car's registration ends in 7IU. Even the car's plate is both 7IU and 71U. Leonard's tattoo of the number ends in 71U, but he says 7IU.
Deliberate mistake: When Leonard takes the photo of his newly acquired Jaguar, the car's hood is parked right up in front of the shrubbery and its shadow is in front, at the hood, seen when Teddy arrived. The actual photo of Leonard's 'new' Jaguar shows it to be nowhere near any shrubs and its large shadow is cast on its right side.
Deliberate mistake: In room 304 Leonard takes the papers that Natalie gave him out of the paper bag, he turns the bag over and written on the bag is "For Leonard from Natalie" with a line drawn underneath the words, It is written completely differently than when it was seen earlier as the waiter at the diner gives the bag to him when he came out of the restroom.
Deliberate mistake: The reminder note that said, "City Grill Main St. today 1:00pm meet Natalie for info.," which Natalie wrote on a pharmacy bag, is seen in Leonard's hand at the Discount Inn just before he goes to meet her at the City Grill and in her bedroom when she writes and hands it to Leonard. The words on the bag are written differently, particularly the words "1:00pm meet Natalie for info."