When Bill throws his cleaver into Monk McGinn's back, the fake cleaver that's thrown can be seen bouncing off the door frame (lower left of the frame) before Monk falls. Later, as Bill is walking up to the collapsing Monk, the prop cleaver can be seen on the ground.
The troops that are sent to quell the riot level their rifles on the command 'Present Arms.' In this time period, 'Present Arms' was a salute and 'Aim' was the proper command for aiming rifles in battle. Also, as the troops approach the mob, they halt before the word 'halt' is spoken. Troops in the era would march until the word is spoken; they do not stop in anticipation of the command.
Pink latex balloons decorate the scaffolding at the hanging. After Charles Goodyear's patent for vulcanization in 1843, some toy balloons were made from India Rubber spread thin in a solution of benzol or coal-naphtha, like the preparation used to waterproof raincoats and galoshes, and then vulcanized; they were thick, more like today's balls or the tough inflated pig bladders used in games before. The latex toy balloon was invented in 1931 by Neil E. Tillotson of Colebrook, New Hampshire. The originals were white or black; colored balloons came along even later, when dyes that would not dissolve the latex were developed.
Prior to the street battle in 1846, Priest Vallon recites a portion of the Prayer to St. Michael: "St. Michael the Archangel, defend us in battle! Be our protection against the wickedness and snares of the devil." The prayer was written by Pope Leo XIII in 1888.
Johnny tells Amsterdam that Bendrick the Cockroach "carries a germ" and "if you try to leave the gang, they say, he hacks up blood on you." The link between germs and disease wasn't known until after Robert Koch's 1876 publication. Louis Pasteur's work, also published in the 1870s, completed the proof to the medical community, though it was called "the germ theory of disease" as late as 1914. In the 1860s, no ragamuffin street kid would have made the connection. He wouldn't have used the word that way, either; the first recorded use outside medical literature is John Tyndall's 1879 Fragments of Science for Unscientific People. Until then, "germ" was the part of a seed from which the plant sprouts.
In the opening scene as Priest and Amsterdam ascend through the catacombs a priest is saying mass and he elevates the chalice while facing the people. Mass wasn't said facing the people until the 1960's.
The hammer dulcimer (string instrument old man is playing) shown just before the fight scene between Amsterdam and McGloin, is of a modern design. Instruments from the time would have been much more cumbersome in design as they would have been homemade, or built by carpenters used to working with furniture.
Amsterdam is offended when McGloin likens his behavior to that of a "chiseler." While the verb "to chisel" meaning "to swindle" existed at the time, the noun form didn't show up into English until the 1880s.
During the outbreak of the draft riots John F. Schermerhorn is seen having a conversation around a billiards table about the state of the riots with, presumably, Horace Greely. Schermerhorn died in 1851, twelve years prior to the draft riots of 1863.
The first dialogue between Tweed and Bill 'The Butcher' in Tammany Hall, Tweed is feeding his birds as he confronts Bill's abuse of the Irish. The line beginning, "You may or may not know, Bill...", clearly does not match his lip movements.
After the dance, when Amsterdam and Jenny are kissing, Jenny says she shouldn't take off her corset because it would take to long to re-lace. Earlier you can clearly see that her corset has a metal closure called a busk in the front of it meaning it is simple to get in and out of without having to lace it every time.
When Bill The Butcher tells Boss Tweed about the streets that make up the Five Points, he names five. There were only three; two continuing through and one ending. Little Water and Mulberry Streets were nearby, but not at the intersection itself.
When Amsterdam is placed on the table, at the pagoda, Bill the Butcher straddles his chest and pounds a cleaver in the tabletop to the left of Amsterdam's head. With the cleaver still stuck in the table, Bill takes another cleaver from his belt and tosses it in the air. As the cleaver descends toward the table, the first cleaver has disappeared and the new cleaver lands in the original cleaver's place.
When Amsterdam meets Johnny for the first time after coming back, they walk along the street and stop. As they talk, Amsterdam's satchel repeatedly moves from over his shoulder to under his arm and back between shots.
At the hanging, when the condemned man at left of screen is calling to his son and delivering his last words, all four men already have nooses around their necks. After he ends his speech and the hood is pulled down over his face, the nooses are dangling free in front of the other three men, and the hangman places the nooses back on their necks.
When the Butcher is back on his feet after being shot in the theater, the blood stain is very different from the one that emerged as he was shot and crouched down. For example, his right lapel is now clean, but it was hit by blood earlier.
When Amsterdam first returns to the Five Points, he is walks alone. Monk stands in front of his shop and looks down at the town. To the right, Amsterdam and Johnny are taking before Amsterdam even meets him.
Just before the draft rioters break into the Schermerhorn house, as the family is sits down to eat, large celadon vases are visible in the dining room windows that overlook the street. Moments later, when the rioters smash through the windows, the vases have disappeared.
When Amsterdam follows Jenny onto the tram after she steals his medal her hand is shown reaching into a man's jacket. The next scene shows her take her hand from her lap as if for the first time and reach into his coat.
About 30 minutes into the film, when Amsterdam is conspiring with the Chinese men to murder Bill the Butcher, he shows them a sheet of paper. When he shows it to them the second time, Amsterdam hands the Chinese man an unfolded sheet of paper, but in the next shot, the sheet is folded, and the Chinese man must unfold it.
After Amsterdam stops Bill the Butcher's would-be-assassin they struggle on the floor. In the wide shot, the assassin's right hand is empty and lying across his stomach. In the next shot, his hand is lying across Amsterdam and has a pistol in it.
After Amsterdam wrestles the assassin, the assassin drops his knife in the wide shot, and it tumbles away. In the next shot, when Amsterdam crawls away with the pistol, the knife is back in the assassin's hand, and he drops it again.
Johnny is forced to meet with Bill, who is seated with 'Boss' to his right. During the scene, the frequent p.o.v. shots change from Bill to Johnny and back and shows 'Boss's' gaze not where it should be on several occasions.
When the Union soldiers take aim at the rioters, each man steps forward with his left foot. During the Civil War, on the command "aim" a soldier would step BACK with his RIGHT foot, bringing it behind his left. Stepping forward would desecrate "the line" (all-important in nineteenth-century warfare).
The movie refers to Anthony, Orange and Cross Streets as being at the Five Points. By the time the events in the movie take place, they had been renamed Worth, Baxter and Park streets, respectively. The city of New York renamed these streets in an effort to change the overall reputation of what was already called Five Points. This strategy failed as the entire area was still as infamous as ever. Most Five Points residents would have still known and referred to the streets by their original names.
During the Draft Riots, a voice is heard speaking as though coming through a PA system. While it's true microphones were first developed in the 1870s as part of the telephone, and that those capable of being a loud PA system were not in regular use until the turn of the century, no actual PA system is ever actually seen; the odd-timbre'd voice begins when a telegraph is on-screen, meaning the words heard are those being sent over the telegraph, not actually shouted to the crowds during the riots.
When Jenny says to Amsterdam and Johnny "I'll leave you in the grace and favor of the Lord" Amsterdam is on the left and Johnny is on the right. When the camera pans back to them, Johnny is on the left and Amsterdam is on the right, but this is not a continuity error. This is one unbroken shot (a pan), not a jump cut, so while Jenny is saying "grace and favor etc." Johnny has moved from Amsterdam's left side to his right side (from the right of the screen to the left, from our POV).
Before the beginning battle takes place, the Priest and his followers stand in Paradise Square awaiting their adversaries. As Bill's men arrive, we see them appear from behind some buildings, and behind these buildings we see a number of large treetops, as if behind the square is a forested area. The problem here is that after the battle, the camera pulls back to show how and where the 5-Corners district is situated in the heart of mid-1840s Manhattan. As the shot zooms out and increases in altitude to reveal the computer-generated cityscape, there are no CGI trees in the scene that correspond with the ones behind the live-action set built to represent the Paradise Square area.
Members of The Dead Rabbits dye red stripes on their shirts to show their alliance but the dye clearly ends at the seam that joins the sleeve to the shirt front. This means the fabric was dyed red before the shirt was sewn together.
When Amsterdam is outside of the draft office the first time, the red haired man behind the draft officer smokes his cigar 4 or 5 times, but never exhales any smoke. Amsterdam is smoking right next to him, and his smoke is clearly visible.
Early in the film, a man in a striped shirt cleaves Priest Vallon in the left elbow from behind with a large curved blade. A cut-away shot shows Bill making a cutting motion at the exact same time. Vallon is holding his cross, and in freeze frame it's obviously him. Bill says "Priest" and takes several steps before he encounters Vallon for the first time during the fight. Vallon, who should be in agony from the blow to his arm, stands and turns towards Bill. Vallon's arm is nearly severed by the opening blow, yet there is no evidence of such a severe injury during the hand-to-hand fight with Bill. As Vallon dies, his coat has some blood in the area of his left elbow, but not enough for the injury as initially shown.
When Amsterdam is preparing for the final fight at the end of the film, his Saint Michael medal is wrapped around his hand and positioned on the front of his knuckles. Afterwards as he continues to gear up we see him take the medal and then wrap it around his hand.
When Amsterdam and Bill face off for the last time, Bill pulls a chunk of shrapnel out from his lower chest. In a shot a few moments before, Bill lies on the ground next to Amsterdam and the shrapnel is clearly missing.