1.In 13 Going on 30, Jenna becomes an adult at the 13:30 mark of the movie.
2.Also in 13 Going on 30, when Jenna thought her boyfriend was an intruder, she grabbed an umbrella. When her father thought he heard an intruder later in the movie, he also grabbed an umbrella.
3.In 50 First Dates, the brain hospital Henry and Lucy go and visit is funded by auto parts tycoon, T.B. Callahan, aka Tommy Boy Callahan, which is Chris Farley's character in Tommy Boy.
4.In Love Actually, the only movie we see that Mark owns is Rear Window, which is about a man who watches the lives of everyone else through his camera lens. This mirrors Mark's life throughout the film.
5.Also in Love Actually, Harry tells his wife Karen that she's "a saint." At the holiday party, Mia — Harry's assistant who he has feelings for — comes dressed as the devil.
6.In Knocked Up, Ben and Alison chose Dr. Howard as their gyno because he claims he never goes on vacation. However, on his desk you can see pictures of him on vacation and he misses Alison's delivery because he's on vacation.
7.In Forgetting Sarah Marshall, Peter drunkenly says, "What's up, Miranda?" as he drinks his fancy cocktail. Cynthia Nixon, who plays Miranda in Sex and the City,walks behind him as he says this.
8.In The 40-Year-Old Virgin, you can see Jenna Fischer (AKA Pam from The Office) in the background in one scene.
10.In (500) Days of Summer, when Tom is watching the sad movie that seems to reflect his life, the projector light is aligned with his head to make it seem like it's projecting Tom's state of mind.
11.In Crazy, Stupid, Love., Emily (played by Julianne Moore and is married to Cal played by Steve Carrell) has a desk placard that says "Associate to the Vice President." This is a nod to The Office, where Dwight was the "assistant to the regional manager."
12.In Friends With Benefits, when Jamie is waiting for Dylan at the airport, a fellow driver had a sign that said O. Penderghast. This is the name of the main character in Easy A and both of these films were directed by Will Gluck.
13.In Crazy Rich Asians, while they're playing mahjong, Eleanor and Rachel's seating positions reflect their origins. Eleanor sits in the dealer's seat, which is East (Singapore), and Rachel sits opposite, which is West (New York City).
14.Also in Crazy Rich Asians, early on in the movie, Rachel's mom tells her to never wear blue and white because those colors are worn when mourning/burying the dead. Later in the film, we see Astrid wearing blue and white when she's burying the fish that was put in her room to torment her.
15.In Pretty Woman, the opera Edward takes Vivian to is called "La Traviata." The opera is about a prostitute who falls in love with a wealthy man, which mirrors Edward and Vivian's storyline in the film.
16.Also in Pretty Woman, Vivian accidentally throws a snail across the room and a waiter catches it and says, "It happens all the time." The same waiter can be seen in Princess Diaries 2 as the guard who catches Mia's bracelet when she flicks it off her wrist who also says, "It happens all the time." Both movies were directed by Garry Marshall.
17.In You've Got Mail, Kathleen buys flowers from a pregnant-looking florist at the beginning of the film. Later in the film, we can see an "it's a girl" sign in the flower shop.
18.In Sleepless in Seattle, Sam tells his son Jonah that one of the things he loved about his late-wife was how she cut the peel off an apple in one long curly strip. A few scenes before, you see Annie peeling her apple in the same way.
19.In There's Something About Mary, when Ted asks Dom about his life he says, "Each day is better than the next." He's basically saying each day keeps getting worse and worse, which is an indicator that he hates his life.
20.In When Harry Met Sally..., Billy Crystal improvised a line in the script which made Meg Ryan laugh — which also wasn't in the script. She then checks with the director off-screen to see if they should cut or keep rolling.
21.In Princess Bride, during the "Miracle Max" scene, they had to replace Cary Elwes with a mannequin because he couldn't stop laughing during the scene.