Continuity mistake: In the first close-up Teddy's eyeglasses are upside down, lying near the tile wall, the next wide shot it's upright, further away from the wall, next close-up it's near the tile wall again, lying on the grout just as it's moving in reverse, then in the next wide shot it's further away from the wall once again, lying on the tile, just before it reverses to go back up onto his face. (00:02:15)
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. (00:02:25)
Continuity mistake: The blood pattern splattered on the tile wall and grout, shown in the photograph that Teddy holds in the opening shot, differs from the pattern that is seen in the reverse shot while Teddy is still lying on the ground, before he even moves. (00:02:25)
Continuity mistake: When Teddy is shown getting shot in reverse, at the start of the film, Teddy's right arm position, Leonard's grip on Teddy's clothing, etc., are distinctly different than in the following scene when he is shown again being shot by Leonard. (00:02:30 - 00:06:15)
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. (00:03:25 - 01:40:55)
Revealing mistake: At the 'beginning' when Teddy and Leonard drive up to the abandoned building with the old truck out front, inside the truck Leonard handles a number of .357 revolver calibre bullets that have apparently not been fired, but you can clearly see the indented primers in the base of the bullets, indicating that they are just inert movie props. (00:04:40)
Continuity mistake: There are scenes in which Leonard is looking at the back of Teddy's polaroid. If you look at the serial number of the polaroid when he is writing "Don't believe his lies" it is a different number than when he looks at it during the beginning of the film. (00:05:15 - 00:07:00)
Continuity mistake: At the beginning of the movie, Leonard looks outside his window and sees room 304 (which will be given later to him on top of his current room) - it is on the same floor he is currently on. Still, when he learns from the clerk that he has been ripped off, we see them both coming out of room 21, which probably is room 221 with the first 2 missing, because it's next to the reception, itself located on the second floor (we know that because from room 304, Leonard only needs to go down one flight of stairs to reach it). Both his rooms, 304 and 221, could not possibly have been on the same floor. (00:06:40 - 00:26:25)
Continuity mistake: The words behind Teddy's photograph, "Don't believe his lies" are written differently on the same photo three times. First, when Leonard reads it at the abandoned building, second, when he writes it and third when he looks at the photo after seeing a copy of Teddy's license while in room 304. (00:07:00 - 00:13:05)
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. (00:11:45 - 00:12:50)
Continuity mistake: After entering room 304, Leonard steps on the bed to put the 4 photos back up on his paper on the wall. In the 1st close-up he puts the Discount Inn and the 2nd close-up he puts up Natalie. Then in a wide shot of Leonard looking at the paper, visible at the top of the paper, in the center, is the photo of Natalie and on its right is the photo of Teddy, already up. In the next shot, the 3rd close-up, he puts up his car. However in the next wide shot ALL three photos that he just put up in the close-ups are GONE. Then in the 4th close-up he puts up Teddy's photo, which was up in the first wide shot. (00:12:25)
Continuity mistake: Under the photo of Natalie, the name Natalie is written. When the photo is seen in room 304, on the wall, then when he finds it while in her bedroom, and when he writes it at her house, the handwriting differs. (00:12:25 - 00:38:35)
Factual error: In the beginning, Leonard looks at a copy of John G/Teddy's driver's license. The expiration date is listed as 2-29-01, but of course, 2001 was not a leap year, so there would've only been 28 days in the month. (00:12:45)
Continuity mistake: Leonard sits down at the table in room 304 and starts to pull out from the bag the info that Natalie provided. His keys are positioned differently on the table in the wide shot and close-up. (00:12:45)
Continuity mistake: In the scene in which Leonard writes on the back of his picture of Teddy, "He is the one. Kill him," we see a shot of Leonard placing the picture on top of his tan jacket on the bed as he goes to write on it. Then, it goes to a close-up of the picture in which the jacket has disappeared and the picture is lying directly on the blue bedspread. It actually happens twice within that same scene. (00:15:15)
Other 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. (00:17:10 - 01:20:50)
Continuity mistake: When Leonard and Teddy are in the diner, after Teddy asks, "You think he's still here? Jon G., the guy you're looking for?" the amount of water in Leonard's glass changes in the wide shots and close-up. (00:23:25)
Revealing mistake: At the diner Teddy puts his fingers on Leonard's pulse and Teddy's watch reads 4:45. Teddy jokes that Leonard probably left his key in his room. Leonard goes back to his motel to find his key and asks Burt for the time, to which Burt replies, "A quarter to one," - 12:45. (00:24:25 - 00:26:20)
Continuity mistake: At the diner after Teddy asks, "Where are you staying?" he wipes his mouth with the napkin. The position of the napkin in Teddy's hand differs in the shot facing Leonard and the shot facing Teddy. (00:24:40)
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." (00:26:15 - 00:30:35)
Answer: The are no alternative endings for this film, all that is on the third disk is the movie played in chronologial order so you can see how things really panned out.