Continuity mistake: When Jack is drawing Rose, the first close-up of Jack's hand shows charcoal on his thumb and nail which vanishes seconds later on the next close-up. (01:23:30)
Other mistake: When Jack draws Rose the hand that is shown in close-up is much too old to be his. [It's James Cameron's hand - still a mistake, but there's why.] (01:23:40)
Continuity mistake: When Jack is preparing to draw Rose, when he says "Try to stay still", on Jack's sketchbook we can see some sort of bookmark or flap. Right before he starts drawing, when he exhales, that little flap thing is missing. (01:26:35)
Factual error: When Jack and Rose are being chased by the bodyguard, they run through the ship's boiler room, prior to winding up in the car. Titanic was fueled by coal, and the boiler workers were called the "black gang" due to what happened as a result of working there. Yet Rose was wearing a pale dress which stayed pristine after going through the area, as did her shoes. She should have picked up at least a little soot along the way, at least on her shoes and the hem of her dress. (01:28:00)
Visible crew/equipment: When Jack and Rose are running from Lovejoy, they stop for a moment on E deck. When they do, look behind them and a member of the ship's crew comes into shot holding a bag of something. When Jack and Rose start running again, this man has disappeared. (01:28:20)
Visible crew/equipment: When Jack and Rose are running away from Lovejoy (Cal's servant/friend), they run round a corner on E-deck. When the camera follows, the camera's shadow can be seen on the wall. (01:28:45)
Factual error: When Jack and Rose are running through the boiler room not only is there no door between boiler room 6 and the cars but the cars were kept two decks higher, and there was a shaft between them. (01:29:30)
Visible crew/equipment: When Jack and Rose enter the car to make love, cameras, shades, boom mic and studio structure are reflected on the brass parts of the car. (01:29:30)
Continuity mistake: Inside the car, Jack places his hand on Rose's shoulder, but a frame later it's on her arm. (01:30:00)
Continuity mistake: Inside the car, Jack asks Rose "Nervous?" and she turns her seriousness into a big smile. Just a frame later, from the opposite angle, she is still very serious. (01:30:10)
Continuity mistake: After the sex scene between Rose and Jack, Rose's hair is wet with sweat. When the two of them appear on deck, her hair is exactly as it was before the sex scene. (01:30:40)
Audio problem: When the one lookout says "b*****ks", his mouth doesn't match what he is saying. (01:31:20)
Continuity mistake: After making love, Jack says to Rose "Don't worry, I'll be all right" and kisses her, sucking the upper part of her lip. When the angle changes, he is sucking the lower part. (01:31:50)
Continuity mistake: At the part when Jack or Rose (I can't tell which) wipes their hand on the fogged up window, they show it again in the next shot and you can definitely tell it's a completely different handprint. (01:32:00)
Continuity mistake: When Hockley and Lovejoy find the drawing of Rose in the safe, Hockley is holding the drawing which has been secured in some kind of brown manila folder. A split second later, Hockley reads the note Rose left while still holding the drawing (and even angrily squishing it slightly with his hand), and it is not in a manila folder. (01:32:40)
Factual error: When the men are checking the store room for Rose and Jack, the men are using huge battery powered bright white flash lights that look like they're from Jurassic Park. Back then they would have produced yellow light. The light used in the movie was a Short-Arc Xenon bulb, you can tell this by both the very high color temperature of the light and the center of the light has a "hole" in it where the actual tube is blocking the beam. Such technology was not around at that time. (01:33:15)
Continuity mistake: When Rose and Jack run outside after making love in the car, you will notice a shot of the men in the lookout tower where you can see their breath due to the extremely cold night. But when the shot goes to Jack and Rose, you will notice that you cannot see their breath but also Rose does not seem to be affected by the cold even though she is wearing a thin dress with no sleeves. (01:33:35)
Continuity mistake: When the two guys in the watchtower on the front of Titanic spot the iceberg, the shot cuts to the helmsman. Behind him the clock says 11:40pm, but when we next see the clock 5 to 10 minutes later its still on 11:40pm even though almost 10 minutes has passed. (01:34:35 - 01:38:50)
Revealing mistake: In the first shot of a sailor watching the ship right in front of the iceberg, the mast has thick blue lines around it and the man's coat and cap swap from black/dark blue to faded blueish colour, all due to the green screen. (01:34:45)
Continuity mistake: When the engine room gets the order to cut power to the engines, the wheel that one of the engineers is turning is black, however a few minutes later the wheel is gold. (01:35:00)
Chosen answer: During the several years it took to construct the ship probably, or in any of the supplies/food brought on board, or in the furniture brought on board. A single pregnant female rat can be responsible for thousands of rats in a very short space of time (the offspring are not too choosy about who they breed with).
Soylent Purple
A pregnant female rat could have made a home in a underneath a third class couch and had the other rats then all the females would have baby rats quickly.