When Connor and Murph are waiting for Rocco to call them, Murph slams his hand down on the phone when he picks it up. The phone has an electric "ring", but when Murph slams his hand down on it, we hear a bell. A phone with an electric ringer would not have any kind of bell inside it.
At the bar, when Murphy speaks to the Russian mob leader Ivan Checkov, Murph refers to him as 'Vanya'. Although a diminutive of the name Ivan, the subtitles, in which Murphy is speaking in Russian, say 'Ivan' rather than 'Vanya'.
Rosengurtle Baumgartner is wrong about what "rule of thumb" means. In reality "rule of thumb" is a medieval term referring to an ordinary, everyday measurement system. The idea that "rule of thumb" condones spousal abuse is believed by many people, but isn't true. The "wife beater's rule of thumb" was invented in 1782 by a humorist, James Gillray, as a metaphor to satirize incompetent legal systems. Many people mistakenly believed (and still do) that he was referring to an existing law.
When the Monsignor relates the story of Kitty Genovese, he mentions that the attack took place "almost 30 years ago" and "in broad daylight." The attack occurred in 1964, a full 35 years prior to the movie taking place, and at 3:30 AM (albeit under streetlights). These errors may have been purposeful to demonstrate that people's indifference continues, and is even greater now.
When Paul Smecker is introduced in the alley, he asks for a Detective Duffy to bring him a "café latte, twist of lemon, sweet n' low." The problem with this order is that a latte is made with steamed milk. The acid in lemons causes the proteins in milk to gather together in clumps, curdling the milk and would therefore not be ordered in a latte.
During the alley investigation, the sunlight and shadows against the building change dramatically as Smecker looks down the alley. First only a strip of sunlight is on the wall, then a huge triangle a few seconds later.
When Il Duce steps forward, he is standing by the middle of the car, looking up with two pistols out. In the next shot with Paul Smecker on his knees, Il Duce is standing at the back of the car, looking down and his guns hidden by his coat.
When the brothers leave the gun store, they are wearing sunglasses, which disappear for the next few shots; even when they walk down the stairs into the basement. When they step into the elevator, they carefully take their sunglasses off.
When Connor is in the police station, on the pay phone, holding the pager with his right hand, the tattoo veritas is on his index finger. When the camera angle changes, veritas is tattooed on his middle finger, then back on his index finger.
During Smecker's investigation of the Russian mobster's deaths, he places a bottle of some liquid he uses on the Russian's hand on the ground about a foot and a half in front of the Russian's body. When the close-up of the Russian's hand is shown, however, the bottle is much closer, then it returns to its previous position on the ground when the shot switches again. Then as Smecker stands to investigate the bullet hole farther down the alley, he leaves the bottle on the ground. The bottle disappears in the next shot as the camera zooms out away from the body.
During the beginning scene in the church you see the church completely filled from the rear of the church. Later when you see the congregation from the front there are less people then what you saw before.
When Connor is straining to get free from the toilet he's cuffed to, the sash of his robe has fallen out of the left-hand loop of his robe and is only being held by the right-hand loop that is facing the camera. When he walks out onto the rooftop with the toilet a moment later though, the sash is strung neatly through both loops.
In the hotel scene with 9 dead Russian mobsters, agent Smecker puts his hands in his hair, with blood on his gloves. (the policemen are seen to wince when he does this). Later on, he is looking up at the hole in the ceiling, and you can clearly see that there is no blood in his hair.
When Rocco rushes into the room and is packing: he grabs some albums out of the rack and packs them. In the next shot they are back again. Shortly thereafter the albums are again gone. The actual selection of albums remaining on the rack varies also.
While Smecker is chastising the precinct for leaking the story to the press, right before he says "They're angels!", his hands come out to his sides. From the front, they are shown palms up, but from the back, they are palms down.
As Connor is carrying the toilet onto the roof, you'll notice that before he drops the toilet, the toilet does not have a seat or lid. After the toilet hits Checkov, it begins to turn towards the camera and a closed toilet lid is fully visible.
In the alley scene with the Russians, when Connor throws the toilet onto the Russian holding the gun to Murphy's head, he scares and fires a bullet, which presumably drills a hole into the dumpster. However, when you watch closely, you can see the gun being fired while aiming downward at the floor, not at the dumpster.
The toilet bowl which Connor first pulls out of the floor appears to be a real toilet bowl. When looking directly down at a real toilet bowl, it is impossible to see all the way though it. The next scene with Connor carrying the toilet, the bowl is definitely a prop. This is evidenced in two ways. First you can see through the bottom. Secondly, when it falls on Chekov, the shattered pieces are too thin. The porcelain on a standard toilet bowl are way thicker. Large chunks of porcelain should have still been visible, when Murphy was recovering Connor.
Before Agent Smecker arrives to the scene, a police squad car is shown parked. Agent Smecker is then shown pulling into the scene and getting out of the same car, but the next shot shows the same scene with the car still parked.
During the flashback of the Lake View murders, the blackboard to the right of Sal has types of smoothies. When Smecker and the other detectives are reviewing the case, the board has different writing and different drinks.
When Connor lifts the toilet away from the wall and his wrists start to bleed if you look closely at his right hand you will see him squeezing blood out of what appears to be a sponge making more blood pool on the floor that that which is coming out of his wrists.
After the shootings take place in the Lakeview Lunch Café, when the news anchor is reporting on-location, a shot of the establishment's sign is clearly visible in which it states: Lakeview Lunch Café, Est. 1947, L.L.B.O., which stands for 'Liquor Licence Board of Ontario' - giving away that this part of the film was shot in Toronto. There is also a quick shot of a TD (Toronto Dominion) Bank. As a final clue, a 'Lakeview' Café in Boston is highly unlikely, given the lack of lakes in the area.
Rocco's shooting at the diner is said to take place on "Comm Ave", short for Commonwealth Avenue. The news caption says the shooting took place in South Boston. Commonwealth Avenue runs east-west through Beacon Hill, the Back Bay, Fenway, and Allston. It goes nowhere near Southie.
When in the alley at the first crime scene, the camera points towards the exit, to the main street. We can see, clearly visible, the front sign of a "Henry's" camera store. Henry's only have stores in Canada.
When Connor is standing above the apartment building getting ready to drop the toilet down on the Russian mobster, there is a second where he looks ahead and Toronto's CN Tower is clearly visible in the top right section of the screen.
When the bar fight scene begins the brothers are telling the Russians some phrases in Russian, which are translated in subtitles. Actually the words that they are saying not only don't respond to the translation, they are mostly made up and make no sense at all.
When the boss of the Russian crime syndicate is first shown, a sign telling the viewer who he is appears. It says "Yuri Petrova", while Petrova is a female Russian surname. (In Russian male and female surnames differ, for example: Petrov - Petrova)
Also in the opening church scene the Protestant, rather than the Roman Catholic, version of the "Our Father" (or "Lord's Prayer") is being used (the Catholic version does not have the "For Thine is the kingdom, the power... etc.", but uses a different doxology slightly later in the liturgy).
Il Duce is being held in a "maximum security" prison. When the guards are transporting him they all have shotguns drawn. In real life, maximum security prison correctional officers do not carry guns within such a close range of the inmates, but from a bit of a distance so as to not allow for such easy access of a firearm for the inmates. The officers in close range of the inmate will, however, most likely have a can of pepper spray pointed at said inmate in transfer at all times.
At the beginning of the film, the audience is informed that the day is St. Patrick's Day, and the location is Boston, MA. However, all of the trees in Boston seen in the initial establishing shot and every shot thereafter are in full leaf, indicating that the actual date must be several weeks after March 17th, when all the trees in Boston are still bare from winter.
The Boston Police Department patches that are seen on uniforms and ballcaps are not the right color or shape of the actual BPD patches. The actual BPD patches are conical and blue with yellow lettering that says "Boston Police, 1630 AD".
During the opening scene the two brothers walk out of a Catholic Church situated at a Back Bay intersection. Problem is, there are no Catholic Churches in the Back Bay. This was intentionally planned when the WASPs designed the Back Bay section of Boston.
Agent Smecker says the bullet heads found in the alley are .50 caliber, but the Desert Eagles used by the Russians are clearly .44 Magnums, one is noted by its muzzle diameter, the other clearly reads ".44" on the nose of the frame.
Arriving at the crime scene, Smecker asks one cop his name. After he examines the scene with the headset on, he suddenly knows everyone's name. However, given his quirky and arrogant nature, it would be typical of him to intentionally ask someone's name despite already knowing it (intended as disrespect, etc.).
When Agent Smecker is investigating the alleyway crime scene it shows that one Russian has boot prints on his back, but in the flash back to the crime scene when Connor jumps on his back, his feet do not make contact. Also, he steps *over* him and never on him when retrieving the weapons, money and pager. At no point did his boots ever make contact with the Russian's back. However, someone else could very well have gone through the alley and searched the Russians for their personal effects.
When Smecker is talking to the brothers, Murphy keeps looking up above Smecker's head. When Smecker is getting up to talk to the press you see a piece of white poster board above his head on the wall with the lines written on them.
During the flashback in which Rocco sits outside the house while assassin eliminates members of the targeted family one can see bright flashes that accompany shot fired inside. However, the assassin is shown using large suppressors that would render the flash almost invisible, especially in broad daylight. Furthermore, discharge of the unsuppressed gun usually produces yellow-red flash, not white, flashbulb-like one.
When we're taken through what happened in the apartment with the eight dead guys, one of the Boondock Saints places a dime on each of one of the dead guy's eyelids. Both dimes are clearly shaking from his jittery eyelids, revealing he's acting. You can tell by the reflecting light off of them.
Right after the bar fight, there is a shot of the alleyway outside followed by the scene where the Russians barge in on the brothers. In the alleyway on the bottom of the shot you can see a gray tarp flapping around. The gray tarp is actually the top of the cushion used for the roof jump.
When Connor and Murphy are fighting in the air duct, their weight shifts the duct to the right. On the left the of the screen a brief glimpse of the set can be seen, revealing the duct simply as a prop.
The goof items below may give away important plot points.
When Rocco shoots the cat, when they're all standing in the doorway to the living room, Murphy has an unlit cigarette in his left hand. They cut back to the cat on the wall, and when it cuts back to them, when Murphy says, "I can't believe that just fucking happened!", he doesn't have a cigarette any more.
When Il Duce steps in front of the Taurus to confront the MacManus Brothers and Rocco, the rear wheel is shown without a hubcap. But in the next shot where Il Duce is shown standing in front of the Taurus in full view, both wheels have hubcaps on them.
When Connor, Murphy and Rocco are cauterizing their wounds with an iron you see Murphy being held down first, the sleeve of his shirt is ripped open and Connor is applying the heated iron. The next person to be held down is Rocco, Murphy is doing the burning and his sleeve is now in tact, with a bloodied bandage around it. When it's Connor's turn, Rocco does the burning and Murphy holds him down, his sleeve is once again ripped.
When Rocco is in the confessional with the priest, Connor enters into the confessional opposite Smecker. Connor then uses his finger to open the divider through the screen. You can clearly see him push the door to his left, the shadow on the wall next to him also moves sideways. Next, you see the priest open the divider to Smecker's confessional by lifting it straight up.