When The Dude is at Jackie Treehorn's and he rubs the pad of paper with a pencil revealing Treehorn's drawing of a naked man, The Dude tears the page off the pad and quickly crumples and shoves the paper into his pocket. Later while in the Chief of Police of Malibu's office and the Chief is going through The Dude's wallet, the same paper he tore off of Treehorn's pad is neatly folded in the wallet, with no sign of previous crumpling.
While the Dude, Walter, and Donnie talk about the carpet pissers at the Bowling Alley, the bowlers in the next lane (they can be seen behind Walter) change in incongruous ways. Watch for the big black guy and the big white guy with the pony tail. Also watch the movement of the waitress, which is incongruous. She covers 20 meters within the time it takes the Dude to say "Fuckin'-A".
When The Dude is in the bathtub smoking a joint with all of the candles lit, the Nihilists come in and throw the ferret in the tub with him. There are four candles in the corner to the left of The Dude. When The Dude starts thrashing around he puts three of the four candles out with the water and when it cuts away then goes back to him, the three candles that were out are lit and the one candle that was still lit is out.
When the blond thug in the opening scene drops the bowling ball, the tile on the floor is different than when he picks the ball off the floor.
After Walter jumps out of The Dude's car, The Dude scrambles across to the driver's side, and the door is already closed.
When Smokey steps over the line, Walter insists he mark it zero and move on to the next frame. Scoring a foul on the first ball actually negates the first roll, the pins are reset, and a second ball is rolled.
When Smokey is supposed to have fouled, there was no buzzer, during league play or a tournament the electric eye is always activated. You can see the bowling alley does have the electric eye down at the foul line. Walter was incorrect to call it a foul.
There is not an apartment or house door in modern times that opens outward (hinges outside), as shown at the Dude's apartment. This is so that thieves cannot remove the door hinges and break in. Even the other apartments at the Dude's residence show hinges inside (door swing inward). Presumably, this was done to make the Dude's floor-tripping device more ridiculous when the two thugs came and opened the door, which swung outward, so that the chair fell with it.
The briefcase that Brandt gives The Dude is not large enough to hold one million dollars in twenty dollar bills. One "Brick" of twenty dollar bills contains one thousand bills. Which is twenty-thousand dollars. It would take 50 (fifty) "Bricks" to make up the one million dollars in twenty dollar bills. Hence, The Dude would have needed a much larger briefcase.
When the Dude, Walter and Donny are eating the burgers they supposedly got at In-n-Out, the cups they drink from are not white with a ring of red palm trees, which is the way the cups are at that chain.
Walter draws the firearm and the Dude says, "Man, they're calling the cops." The cops show up as they are leaving. A call from Smokey and Dude and Walter's tournament advancement imply that they stayed long enough to win the round. This is presumably a sly comment on the lethargic response time of LAPD to what they consider a non-urgent call.
When the Dude is on the phone with the kidnappers, a dial tone is heard each time they hang up. However, he's not on a cellphone as some may think, rather he is on a portable car-phone. Unlike a cellphone, the car-phone would indeed have a dial tone.
The movie is said to take place at the time of the first Iraq war in early 1991; many references indicate that it's set a few months before, during the troop build-up in late 1990. But when the Dude makes out a check at the beginning of the movie, it's dated 9-11-1991. This is not necessarily an error, but rather a subtle joke to establish that the Dude is so cheap, broke, and blithely unconcerned about potential legal trouble that he's perfectly willing to post-date a check for under $1 by about a year.
When the Dude is thrown in the back of the Limo while holding his White Russian, plastic wrap can be seen covering the top of the glass, preventing a complete spill of the drink.
At the end of the movie, when the Dude and Walter discover Bunny's crashed car; the car's brake lights are illuminated (it's not due to her headlights because her third brake light is on), despite the car being empty (so there is no one to hold the brake pedal down).
The handwriting on Larry Sellers' homework is the same as the teacher that has marked it.
The ball that the Jesus rolls down the lane is on lane 23, yet the lane number is reversed, as is lane number 24, indicating a flipped shot.
In the opening credits, a big black guy throws a seven-ten split (his ball changing color from the throw to the strike, as noted in "goofs"). The first frame showing the ball striking the leftmost pin reveals that the pin isn't on the dot marking its official position. It's a little ahead of and to the left of the dot, hanging over the gutter, and the ball strikes it from the gutter: the shot is rigged.
The calendar on Francis Donnelly's desk at the mortuary says February 1997, though the movie is supposed to be six years prior to that.
The song, "My Mood Swings" by Elvis Costello is heard through the Dude's headphones at the doctor's office. The song was recorded in 1997, 6 years after the setting of the movie.
Smart Balance is on the grocery store shelf at Ralph's in the opening scene of the movie. This product didn't come onto the market until 1995, though the film is set four years earlier.
The first sex offender laws, like those which would require Jesus Quintana to notify his neighbors of his paedophilic record, weren't implemented in California until 1996.
Jesus is shown having to notify his neighbors that he is a sex offender. While California has had a sex offenders registry since 1947, it did not have a "Megan's Law," allowing community notification, until 1996, well after this movie is set. Furthermore, it is law enforcement, not the offender, who notifies that community.
When Walter is smashing the red car with the crowbar, the other man runs out shouting at him, but his lips don't actually move.
At the hand-off, the kidnappers' dirt bikes have single cylinder engines but the sound is that of four-cylinder engines.
When The Dude is talking to Da Fino in his car through the open driver's side window, we hear music playing on the car stereo. When Da Fino gets out of the car and the door is shut behind him, the volume of the music drops as if the window were shut.
When the Dude calls Walter on Shabbas to pick him up after helping Maude conceive, his mouth eventually stops matching his words.
When the Dude is told about the kidnapping, Wolfgang Amadeus Mozart's Requiem is playing in the background on Big Lebowski's HiFi. However, the timeline of the music does not correspond to the actual conversation.
After Jesus's introduction, the dude shows Walter the pager that Lebowski gave him. While fixing the pager to his shirt's neck-hole, he speaks directly into the lavalier microphone under his shirt, making his voice louder and slightly distorted.
When The Dude and Walter are making the money drop off, after Walter jumps out and The Dude crashes the car, when The Dude runs out saying "We have the money," police lights blocking off the road they are filming on are clearly visible.
When The Dude is driving, and first notices the blue Volkswagen following him, the hood-mounted camera equipment is reflected in his sunglasses.
In the dream sequence when Lebowski glides down the aisle through the dancer's legs you can see the mount holding him in horizontal position under his shirt.
After the introduction of "Jesus" there is a shot from left to right, ending with Walter Sobchak. You can see a reflection of the cameraman in his left eyeglass.
The In-N-Out Burger in North Hollywood is at 5864 Lankershim Blvd, 91601, not "on Radford" or "on Camrose", as Walter or The Dude think.
There is no explanation how Maude would have known to have called the Dude at the bowling alley, or, even more, how she knew he'd be there at that moment.
Before the Dude's car is stolen from outside the bowling alley Walter makes reference to having a million dollars "in the trunk". Later, when the car is recovered by the LAPD, the Dude looks frantically into the back seat and declares that his briefcase is missing. He never opens the trunk.
After Walter bails out of the car, he limps favoring his left leg. That night after bowling, when walking away from the lanes, he favors his other leg.
In the bathtub scene and later, The Dude refers to the Nihilists' ferret as a "marmot"; Walter refers to it as an "amphibious rodent". The animal was not a marmot but a ferret; marmots are rodents but ferrets are not; and neither animal is generally aquatic. (Walter is correct that neither is legal to keep as a pet in California.) The script originally called for a marmot, but when it was realized how big these animals are, a ferret was used instead. The dialogue was left unchanged because the Dude wouldn't know any better.
When Marty invites The Dude to view his performance, he says it will be "on Tuesday night." This night continues on, ending with The Dude asking Walter to pick him up, to which Walter replies that it is "Erev Shabbos." Erev Shabbos is observed on Friday night.
Walter has no problem pulling out his gun over a bowling rule, but the gun is nowhere to be found when he, the Dude, and Donny were confronted by the nihilists, which would've been the most perfect time to use it.