When Mei is first introduced walking down the street, the camera zooms in on her flute case, and one can see all the various references to cultural events of the early 2000s such as stickers about "Y2K-A'OK" and "saving the whales", which was a serious environmental crisis in the early 2000s.
Also a Genius Bonus: In the opening montage when Mei is on the streetcar heading to school, she pulls out a page of homework and starts working on it. The page is titled "Practice Test: Solving Quadratic Equations Algebraically". The visible problems are all perfectly reasonable ones for a test on that subject.
When Mei gets off the streetcar in Chinatown, a sign in the background reads "Bao Restaurant"; Bao being the title of a short film that director Domee Shi had made with Pixar in 2018.
Coincidentally, as of 2022, there actually is a "Bao Restaurant" near the intersection of Spadina Ave. and Dundas St. West which is where Mei gets off as per Word of God. Granted, the restaurant wasn't there in 2002 but it does predate the film.
The school sign reads "Canadian Indigenous People's History Month".
On The Twilight SagaParodyNightfall book Priya is reading when she's introduced, the title has "Final Chapter" above the series title, with the writer being named "Roberta Moyer", the tagline on the back cover being "Why is everything you remember not the truth?", and one review if one zooms in, reads, "SPELLBINDING. You won't be able to put the book down. — Author's grandmother".
Right after Mei wakes up as a panda for the first time, she glances toward her door and her dresser is visible devoid of any hairbrushes. It is only after she rushes back into her room that hairbrushes make their appearances, ready to be used to brush Mei's fur. Unless Jin put the hairbrushes there between sneaking away and showing up with the fire extinguisher, they seem to simply materialize.
When Priya is giving Mei deodorant after Abby comments that she smells, if you look closely you can see that the deodorant appeared out of thin air.
When Mei takes the deodorant, she starts applying it without appearing to take the cap off first; the cap simply ceases to exist until she goes to replace the cap whereupon it materializes in her right hand.
When Mei-in-panda-form is running down the school hallway and runs into the boy with the trombone, on the wall behind her is a typical "motivational poster" which reads "DARE to be DIFFERENT — DARE to be YOU", which is strikingly germane to the movie's main Aesop.
Stacy, the blonde schoolmate that witnesses Mei's panda form, can be seen to have an insulin patch on her shoulder.
While Mei is panicking after turning into her panda form and running across the area, one of the things she knocks down is a diner sign that says "Drop in anytime".
When Mei is pleading with her mother to let her go to the concert, look very closely at the 4*Town brochure Jin is reading. The title is partly hidden by his hand, but enough is visible to read "4*Town: Why I Must Go!" — the same as the title of Mei's slideshow.
After Mei throws a dodgeball at Tyler and her friends drag her away, Stacy and her friend share a brief look, implying that they saw her partially transformed panda arm and explaining why they showed up in the bathroom so quickly.
The camera Miriam uses to take pictures of kids with panda-Mei looks like a Polaroid Instant Camera. Although they're now considered obsolete, in 2002, Polaroids were a common (and great) way to get printed pictures fast.
When Mei tells Tyler to buzz off after learning about the 4*Town concert being the night of the ritual, he actually looks legitimately hurt rather than just annoyed before two other kids egg him on to insult Mei more.
At Tyler's house, when the furious Ming is yelling at Miriam, Priya, and Abby, for a moment Ming's panda-talisman necklace looks like a face with glowing red eyes. It might be a trick of the light ... or it might be a sign that her panda spirit is responding to her emotional state, foreshadowing the moment at the failed ritual when Ming's talisman breaks under the pressure of her rage.
During both red moon rituals, if you look carefully at the design inside the circle you can see that it resembles a taijitu symbol, but one side of the symbol is a stylized drawing of a red panda while the other is a stylized drawing of a human.
At the concert, as Grandma Lee and the aunties start singing, on the SkyDome wall behind them is a banner with the name of the concert: "4*TOWN BREAKING FREE TOUR '02". Going to the concert is the key event in Mei breaking free from her mother's control.
Grandma Lee's poker hand in the card game at the end can be seen to be four 4s and an ace. She got four of a kind and still lost, even though there are only two other hands that can beat such a combo. She wasn't kidding about her new 4*Town talisman being unlucky. Furthermore, the winning hand can be seen to be four eights — and in traditional Chinese numerology, 8 represents wealth or success.
When Mei is rushing home, right after she somersaults under a bundle of poles, she bends down to glance at a can littering the sidewalk. This reinforces her character trait of being a staunch environmentalist as most people wouldn't have noticed the litter even if they weren't in a big hurry.
When Mei first discovers her double jump ability (granting her Not Quite Flight), an Air Canada billboard can be seen which says "Fly with us".
In the same shot, observant viewers will notice Mei is no longer wearing her inner white robe even before she discards her red outer one.
When Mei pulls her friends into her room to shush them, their spines seem to bend 180 degrees backwards in order to fit through the window.
When Miriam hands Mei the note saying "your mom is OUTSIDE", the other side of the paper can be seen with the previous notes written on it.
Mr. Gao's balcony, seen when Mei jumps over it, has a red panda mask hanging on the wall, Foreshadowing that his connection to the Lee family goes deeper than just using the temple to play chess in.
When Ming drives off after being caught spying on Mei by the security guard, she comes within centimetres of hitting him with the back of the car.
When Mei struggles to keep her emotions in check like when she is goaded by Tyler during the dodgeball game, her hair expands and becomes frizzy.
When Mei pandas out in the bathroom, at Abby's request, using her lust for Robaire and mermen, little heart shaped poof clouds show up right after the main poof cloud dissipates.
The dollar signs in the eyes of Mei and her friends when they get the idea to hustle the panda are blue to match the colour of Canadian $5 bills.
In the shot of the falling coins during the panda hustle montage, the loonies have a chicken instead of a common loon and the toonies have what appears to be a dog instead of a polar bear.
At the beginning of the scene where Mei and her friends are making keychains, they all have bags under their eyes.
When Tyler successfully blackmails Mei into talking with him, he looks self-satisfied for a moment, suddenly realizes Mei is right behind him as an angry panda, and faints with the toothpick he was using spinning in midair briefly before dropping.
During the scene where Mei and her friends are on Tyler's house's roof, right after they lie down, the shot of the skyline features a shooting star.
The first slice of Tyler's birthday cake that Mei eats appears to have only white icing on top instead of including blue icing or part of the image on the cake as would be expected given which slices are missing when she goes for another one.
When Mei jumps from Mr. Gao's rooftop toward the temple, two men can be seen walking on the sidewalk hand in hand implying that they are a gay couple.
When Mei peeks out from beneath her blanket right after Jin says "This happened already", her hands appear to be swapped based on the location of what looks like her thumbs.
When Mei pandas out while dancing to 4*Town during the panda hustle montage, she launches herself high enough to poke her head through the false ceiling. Also, after she accidentally bats Miriam's panda headband off her head, she cringes for a moment before poofing back.
During Panda Ming's rampage at the concert, eagle-eyed viewers will spot Tae Young sucking his thumb while dangling from the ceiling by his harness.
The first time Mei transforms back to human and when she transforms back to land inside the SkyDome her hair is double its normal length for a few frames.
During Tyler's birthday party, a trio of Mei's classmates are sitting on a couch when Mei grabs on to the one on the end and pulls her onto the dance floor. The one sitting in the middle grabs on to the one being pulled by the arm and the one on the other end by the ankle resulting in all three being pulled with the one on the end being subject to an Ankle Drag. All this takes place in the space of a second.
Pads are not the only menstrual product seen in the film. A pad and tampon dispenser can be spotted in the school bathroom during the scene where Mei hides there after turning into a panda for the first time and the one where Stacy and her friends catch her there in panda form.
At the concert, Tyler wears a 4*Town themed basketball jersey except when he helps out with the ritual when suddenly he is shown wearing his usual Toronto Raptors jersey and he has bandages on his arms. He's back in the 4*Town jersey in the Group Picture Ending. This can be chalked up to a last minute change to how Tyler got to the concert.
.