Continuity mistake: When the three guys who aren't Bill Murray and so don't mind wearing overalls and carrying backpacks pull over as Peter fails to hail a cab, the car's license plate says "ECTO 2", but in the rest of the movie the plate is "ECTO 1A" (apparently because the former would have conflicted with the cartoon, where ECTO 2 was the mini-helicopter). (00:57:45)
Continuity mistake: The position of the socks (or whatever they are) sticking out of the suitcase when Peter presents the suitcase to Dana changes between shots. The one on top stick more in the second shot. (00:54:00)
Continuity mistake: When Peter talks to Dana and shows her the suitcase with her stuff (they sure seem to come and go as it pleases them from her home), Sigourney Weaver is holding the towel in a different way depending on the camera angle. (00:53:40)
Continuity mistake: When the Ghostbusters with their proton packs walk away from the car and get to the museum the morning after the bathtub incident, the people in front of the museum and on the stairs change at the cut. (00:50:25)
Continuity mistake: When Ray passes the paper with Vigo's biography to Peter outside the museum, the passers-by change at the cut. (00:50:00)
Continuity mistake: Peter leaps on his own bed after telling Dana that she can treat his house as her own. Between shots, the spare clothes tucked under the covers and those lying on the box by the window change entirely. (00:48:45)
Continuity mistake: When Dana tells Peter that she thinks the painting is watching her, Peter turns towards Vigo with the whole body. In the close-up, he's glancing at the painting sideways facing Sigourney Weaver. (00:44:25)
Continuity mistake: Peter drops by the museum to see Dana. As he enters room 304, a worker there is wheeling away a big crate. Cut, and the crate spun 90° (just check the stickers and the "Keep dry" writing, first on the right side, then on the side facing the worker). (00:42:40)
Continuity mistake: The prosecutor interrupts Tully being fed every line saying that he's "leading the witness." She leans on the table, but before the cut ("Mr Tully...") you see her pull back and begin to raise her hands. Next shot and she is still palms flat on the table. (00:30:25)
Continuity mistake: After they trap the Scoleri Brothers, Spengler lifts his foot from the trap mechanism. In the immediate angle his foot is still on it, and he is lifting it again.
Continuity mistake: Before the trial, Tully leans over the table and tells the boys that he got his law degree at night school; Ray in the reverse shot is holding his pencil at table level, while it was well under it out of frame in the previous. (00:28:00)
Continuity mistake: In front of the puppy testing box, Egon tells Dana not to worry and lowers his instrument. Dana gives him her number in the next shot, which begins with Egon holding the device higher again. (00:07:15)
Continuity mistake: When the prosecuting attorney walks up to the witness stand with Peter on it, she stands off to the side. When Peter puts his hand on hers in the next shot, she's standing in front of it. (00:31:25)
Continuity mistake: When Lady Liberty shows up on the streets, she makes a left turn towards a big avenue. From the ground shot the police cars and motorcycles have moved ahead and the road is clear. From the aerial angle the cars and motorcycles are right next to the statue's feet. (01:29:35)
Continuity mistake: When Louis is saying 'his place at 8' there is a guy in the background on the right hand side on the sidewalk. When it cuts to the long shot and he is almost hit by the taxi, the guy is gone. (00:56:00)
Continuity mistake: When Ray calls New York "a burned-out burg", a group of firemen behind the Ghostbusters is starting a fight. Cut to Ray in close-up and the fun background activity is no more. (01:25:50)
Continuity mistake: The first shot of Lady liberty walking down the streets and looking down at people is an obvious human face in disguise and makeup. In the close-up shot, it is a mask/miniature that doesn't look like the previous one, but does resemble the real Lady Liberty. This is not due to the statue being animated by ghosts, for the mistake takes place between one shot and another (besides, the statue is animated all the time), but because the FX was achieved combining a human in disguise and a miniature set. (01:29:50)
Continuity mistake: When Dana is watching the couple arguing she has her arms crossed. A frame later, from a different angle, they are not.
Answer: Because she knew Peter would want to get involved. They didn't part on good terms and she hadn't spoken to him since her marriage. She just thought it would be awkward to see him again.
Bishop73