In the scene where Johnny and Baby are practicing dancing, and she keeps laughing when he runs his arm down hers, it was not part of the scene; she was actually laughing and his frustration was genuine. They left it because it was effective. Her falling over in this scene was unplanned too.
The very famous scene where Johnny and Baby are practicing their dancing and they are crawling towards each other on the floor wasn't intended to be part of the film; they were just messing around and were warming up to do the real scene, but the director liked it so much he kept in the film.
Although it is never explicitly spelled out, the medical procedure for which Penny needs Baby's money is an illegal, back-alley abortion (the doctor is described as having only "a dirty knife and a folding table"). In 1963, when this movie is set, abortion was still illegal in the US (it would become legal in New York State up to the 24th week of pregnancy in 1970 and across the country in 1973 with the Roe v. Wade Supreme Court decision), and women seeking abortions either went to a country where they were legal or (much more commonly) went to an abortionist who was willing to perform the procedure in secret. Since abortion was illegal, it was medically unregulated and often performed by people who were not even actually doctors (some women even tried performing the procedure on themselves), and thousands of women every year were killed, maimed, or rendered sterile from septic or botched illegal abortions.
While the exteriors and cabin scenes were filmed at Mountain Lake in Virginia, the lake scene was filmed at Lake Lure in North Carolina in October. There are no close-ups because the actors were so cold that their lips were blue.
According to a December 2008 interview with Dirty Dancing (1987) screenwriter Eleanor Bergstein, the characters of Baby and Johnny were both influenced by Bergstein's own biography. Like Baby Houseman, Bergstein came from a liberal Jewish family who visited Catskills resorts during the 1960s; her father was a doctor; she was nicknamed "Baby" until she was 22 years old; and her real first name was the same as a famous woman with strong ties to the Franklin D. Roosevelt administration (i.e., Eleanor Roosevelt). Like Johnny Castle, Bergstein was a skilled "dirty dancer" who learned at house parties and later became an Arthur Murray instructor.
During the scene where Baby and Johnny are dancing in the woods and later in the water - since that part of the movie was shot in October at Mountain Lake Virginia, which is when all the leaves on the trees start changing colors - the trees all around the lake and for that scene were spray-painted green due to the fact that the time frame of the movie was set in the summer. If you look closely during that scene in the woods, you can see leaves falling off the trees - this doesn't happen in the summer.
The film was re-released in 1997 solely due to a petition led by late-night talk show host Conan O'Brien in which he asked viewers to send letters calling for the film's re-release. When exhibitors finally agreed, O'Brien joked that he actually didn't like the movie all that much.
Baby tells Johnny that her real name is "Frances, after the first woman in the cabinet." Frances C. Perkins was the U.S. Secretary of Labor from 1933 to 1947. She was appointed by President Franklin D. Roosevelt during his first term, and served throughout all four of his terms and two years into Harry Truman's presidency.
Lynn Lipton, the actress originally cast as Marjorie Houseman (Baby's mother) was replaced early in the filming with Kelly Bishop, who had originally been cast as Vivian Pressman (the "Bungalow Bunny"). Left without an actress to play Vivian, the producers cast Miranda Garrison, the film's assistant choreographer, in that role.
Max Cantor played the role of Robbie Gould in the film. Max was the son of Broadway producer Arthur Cantor. They lived in the Dakota Apartments on West 72nd in NYC with John Lennon and other residents. Max attended Harvard University and died of a heroin overdose at the age of 32.
The book that Robbie tries to lend to Baby as an explanation for his refusal to help Penny is 'The Fountainhead' by Ayn Rand. Rand was the creator of a philosophy called Objectivism, which holds (among other beliefs) that it is more important for a person to be concerned with his or her own well-being rather than to try to help others. Some of her adherents (including, apparently, Robbie) interpret her books as justification for selfish and self-serving behavior and the disavowal of responsibility to others.
The trivia items below may give away important plot points.
Toward the end of the movie, Lisa, Mr. Kellerman, and several others sing an anthem to the Kellerman's resort ("Join hands and hearts and voices/ Voices, hearts and hands...") in the talent show. This song's lyrics were written for the movie, but the tune is a traditional one (known variously as "Amici" or "Annie Lisle") from the early 1800s that has been used as the basis for the alma maters for many well-known American universities, including Cornell University, The University of Alabama, and the University of North Carolina at Chapel Hill.
In the last scene, on-screen Mom Kelly Bishop says of Baby's dancing, "I think she gets it from me." Not so fast, Mom! Bishop was a well-known Broadway singer and dancer, but on-screen dad Jerry Orbach began his career in Broadway musicals and the father of Jennifer Grey is Tony- and Oscar-winner Joel Grey. Their most famous Broadway musicals - 'A Chorus Line' for Bishop and 'Chicago' for Orbach - had a famous rivalry for box office receipts and awards when they opened within months of each other in 1975.