Continuity mistake: When the first police car makes a U-turn, to chase the Fratellis, the squad car's front passenger window is rolled up, as the officer's hands are on the steering wheel. But in the next interior shot, facing that window, it's rolled down - there's even a black wire hanging over the bottom of the open window, to the left. (00:02:30)
Continuity mistake: When Mouth goes down the hole in the fireplace passageway, the cooler base is right beside the fireplace, but when Mikey pushes Data and his backpack into the hole, the base is farther away. When Brand pulls the log holder over the hole the base is back, right beside him, but when Chunk heads for the basement window the base is farther away again. (00:45:45 - 00:47:20)
Continuity mistake: In the first overhead shot of Chester Copperpot, his entire ribcage and his right arm bone are visible. In the following shots the boulder lies more than halfway up his ribcage and the arm bone is not visible any longer. (00:53:35)
Continuity mistake: When the Fratellis drive away from the Lighthouse Lounge with the corpse wrapped in the black plastic, the boys duck down behind a rock and a large piece of driftwood. Their positions are completely different between the front and back shots. (00:36:45)
Continuity mistake: There is a rather tall plant beside the Walsh's front door, in the corner, that keeps moving from the corner to the front of the draperies, then back again, throughout the early scenes. (00:06:50)
Continuity mistake: After removing the 'copper bone' necklace from Chester Copperpot, when Mikey puts the necklace around his neck, the cord's knot moves farther up between shots.
Continuity mistake: When Jake Fratelli searches through Chester Copperpot's wallet, it faces the opposite direction between shots - note the driver's license. (01:08:30)
Continuity mistake: Just as Data hands Mouth the lantern and Mikey tells him to translate, Mikey stands between Data and Mouth, but next shot as Mouth says, "Copper bones. Westward foams. Triple stones," Mouth is between the other two boys. (01:09:40)
Continuity mistake: When Data crashes through the screen door, sending Chunk to the floor with the statue, in the first shot there is a long bright stream of sunlight shining on the carpet, between Chunk and the stereo which disappears in the next shot. (00:08:55)
Continuity mistake: When Mikey pulls the cord to release the bowling ball, the rocking chair is parallel to the railing, facing the porch, but in the opening shot of the house it was closer to the stairs and facing the yard. (00:05:10 - 00:07:35)
Continuity mistake: When Mouth stands by the door cracking up at Chunk's 'Truffle Shuffle' and in more following shots, there is nothing on the wall behind him between the hutch and doorway. After Data breaks through the screen door there is a large painting hanging there. (00:07:30)
Continuity mistake: When Brand runs down the stairs to take the paperwork from Mr. Perkins, the large hanging plant that should be over Mikey is gone, but it was there when Chunk arrived and is back later. (00:07:25 - 00:20:25)
Continuity mistake: When Chunk is picked up on the road by the Fratelli brothers and thrown into the back with the corpse, he starts screaming. His red jacket hangs off his shoulder, but rights itself between shots. (00:49:40)
Continuity mistake: On Inferno's deck, when Data stubbornly takes a stand against the Fratellis, Mikey's and the others' facial expressions and positions repeatedly change between close-ups and wideshots.
Continuity mistake: When Troy sends the bucket down the well, in shots facing Andy and the rest, she stands behind the bucket, but in the shots facing Mikey as he tries to convince them all to continue on, Andy's left foot is atop the bucket, and so on.
Continuity mistake: After Mikey sets off the falling boulders by pulling the wire, when Brand climbs up to move the rock Stef and Andy are standing about four feet apart, but in close-ups they are shoulder to shoulder, and so it goes over and over again. (00:57:20)
Continuity mistake: After they find the skeleton key, when Mikey lifts the string in the dirt, which triggers the scythe to cut the rope, the rope differs between shots. (00:56:20)
Continuity mistake: When Stef finds the newspaper with the mugshots over the telephone and shows it to the others, how the newspaper is folded differs between close-up and wideshot. (00:42:50)
Continuity mistake: When Chunk is in the freezer collecting a bunch of the ice cream in his arms, their positions change between the wideshot and close-up, when he sees the frozen corpse. (00:43:35)
Continuity mistake: When the Inferno sails past everyone on the beach, in the close-up of Mikey blowing a kiss and saying thanks, he has a blanket wrapped around him, but next wideshot the blanket is on the rocks, at his legs. (01:48:10)
Answer: According to Mikey and Mr. Walsh, one of his crewmen must have taken the map and fled when One Eyed Willie was murdering his crew. This is substantiated in the novelization.