Audio problem: When Unger shoots his pistol into the sewerpipe in the basement, his gun has a silencer but the gunshot you hear is not silenced.
Continuity mistake: Alex's Dad hangs up the steamer in the attic, when Alex informs him that his taxi arrives. The metal holder the steamer hangs on changes position with every shot.
Factual error: In real life (there are a couple of scenes like this) snow doesn't fall from the sky at the intensity it was from clear skies.
Other mistake: When Alex's mum calls the woman thief at the scene where the thieves are redirecting the phone calls, the screen shows Alex's mum dialling a number. The call is redirected to the thief's mobile, but notice that on the computer screen, "Interrupt" is spelled wrong, and instead is spelled "Interupt".
Continuity mistake: When Miss Hess leaves the plane after landing in Chicago, she takes a scarf out of the Parisian bag she has accidentally picked up. Surely she would have noticed the items within the bag were not hers when she put the scarf in the bag?
Continuity mistake: In the scene where Alex's mum is about to leave his room after applying lotion to his chest. Alex's hair is slightly scruffy - when the shot comes back to him after being on the mum his hair is combed and neat.
Continuity mistake: When the luggage goes through the scanner at the start of the movie the bad guys put their toy car on the belt followed by a brown bag. Scene then cuts to the old woman, and she picks up the bag which is the same bag as the bad guys', followed by a blue one. When the bad guy pick their bags up it's still in order they put it on, nothing swapped.
Character mistake: When Jernigan chases the car, he tells the team, "It's heading south on Adams." The toy car then turns left, which means that the car should be heading east. However, Jernigan tells the team that the car is headed west.
Continuity mistake: When Beaupre and Unger get smashed by the trunk of books, it shows them clearing the books off them. When they are shown again, Beaupre still has a book on his chest.
Revealing mistake: It's obvious the snow is fake. You can see when Alex runs outside in his pajamas.
Other mistake: When Jernigan says, "Gotcha" when Alex comes into the room and Jernigan falls, it shows him falling but his expression doesn't seem like he is actually scared.
Continuity mistake: The main bad guy has Alex cornered in Mrs. Hess' garage. Look at the clear plastic cup behind Alex. One shot the cup is upright, the next it is on its side.
Continuity mistake: The scenes where the bad guys get into Chicago are in daylight, but when they are "chasing" the taxi cab it is nighttime.
Continuity mistake: When the police are arriving at the end of the movie (behind the snow ploughs), there is an overhead shot showing sunlight shining onto the street. Every other shot in that exact scene is otherwise grey and cloudy.
Continuity mistake: When Alex runs into the garage towards the end of the movie, we see sunlight shining in through the window. Wasn't it just grey and snowy outside?
Audio problem: When Mr. Unger is being led away after his arrest, watch - he's looking at the policeman holding his arm, talking and making gestures with his hands...yet there's no sound that goes with it.
Continuity mistake: When Alex first takes out the bubble-squirting gun and threatens Olek Krupa's character with it, the muzzle looks like what one might see on a real gun. However, when we get a closeup of it after Alex shouts at Olek Krupa and chases him away, the muzzle has a gaping hole in it, because it's a different bubble-squirting gun.
Continuity mistake: Near the beginning, Beaupre and Co. follow a taxi driver to its station and we see it park. It pulls right up to a metal fence. However, when Jurnigen and Unger approach the taxi driver a moment later we can see in the background that the fence is a good distance away from the car.
Continuity mistake: When Dupre knocks the washing basket off of the side, on top of the car, we see the basket land upside down, but in the next shot it is on its side.
Answer: It was Jernigan who thought there was a woman in the shower and he couldn't take the risk that if it was a woman, that she would eventually get out and see intruders in the house and call for the police. The only option open to Jernigan would be to kill her so there'd be no witnesses.
No it was Beaupre who thought there was a woman in the house.
I've seen the movie and I can confirm that it was Jernigan who opened the shower curtain because he thought a woman was in the shower.