Continuity mistake: When Harry and Sally are at a restaurant having lunch (this is when she has the fake orgasm), if you look at Sally's sandwich when they show her from behind, you will see that where she has bit into the sandwich has changed. First the bite is on the right, then the middle, then the left, etc.
Factual error: When Harry and Sally leave the University of Chicago to drive to New York, they pass through downtown Chicago on Lake Shore Drive, which actually would take them 10 miles out of their way.
Revealing mistake: During the Lake Shore Drive scene, during the late 1970's, check the model years of the passing cars. There's at least one Ford Taurus which did not debut until the 1984 model year.
Continuity mistake: When Harry and Sally are in the car driving to New York, in the front shots you see the car has no rear-view mirror.
Continuity mistake: During the fake orgasm scene, the bite on Harry's sandwich increases and decreases between shots.
Continuity mistake: When Harry and Sally are on their way from Chicago to New York, Sally's hair changes. You have to really look for it, but watch the curl in front appear and then disappear.
Continuity mistake: In the fake orgasm scene in the restaurant, when Meg Ryan holds her sandwich up there's one bite out of it, then it flicks on to Billy Crystal and when we see the sandwich again it has two bites out of it, but there was no time for her to have eaten any more. Later it has one bite again.
Answer: Sally could be upset for having to drive Amanda's boyfriend, or it could be awkward because they don't know how to say goodbye. There could be a number of reasons why things appear tense between Sally and Amanda, just not explained.
That was a big question mark for me as well when I watched the movie, to the point that I had to re-watch the beginning because I was sure I had missed something; their behaviour doesn't make sense.
Sammo ★