When Christie Masters is making her speech at the real high school reunion, the beer on Heather Mooney's dress appears before she spits it out.
When Heather demonstrates her quick burning cigarette, it gets very short, but in the next shot is at full length again.
When Romy and Michele are leaving for the reunion in the Jaguar, there is a television box in the back seat behind Romy. When they drive off the box disappears.
When Romy and Michele are looking at Vogue magazine, the cat licks its leg or the ham, depending on the shot.
After talking to Heather, Romy makes the next woman wait. When the woman's back is to the camera, her elbow's on the counter, her chin being supported by her hand. This is not so when she is facing the camera.
When Toby asks Heather and Sandy if they want to name all 50 state capitals at the prom, Sandy incorrectly says "Albuquerque". Albuquerque is not the capital city of New Mexico, Santa Fe is.
Christie sticks magnets to Michele's back brace as a prank. Back braces are made of aluminum, so the magnets would not stay attached.
Michelle tells a passing motorist she was trying to scare his child. At highways speeds with windows and a top down it would have been impossible for the motorist to hear her, especially when she is shown to speak in a normal speaking voice.
Billy's abdominal fat is not in proportion with the rest of his body including face which appears to be well toned, indicating he is wearing a prosthetic (fake) stomach.
Before they dance together, Sandy takes off his jacket, Romy and Michele both take off their shoes. After they dance, they walk out of the ballroom, leaving their things behind. When they get outside, jacket and shoes reappear.
When Romy weighs herself at the gym, the scale tip is all the way down, indicating she over-weighed herself.
At their prom in 1987, Romy intentionally has her hair styled like Madonna (the "A group" girls even sneer at her and Michele whom they refer to as "the Madonna twins"). However, Madonna didn't do the blond ponytail look until her Blond Ambition Tour in 1990.
At the real reunion, after being caught telling a lie Romy says, "Now we're just a stupid joke just like we always were." One can clearly see by her lip movement that she is saying something else (possibly the 'f' word).
When Toby announces Sandy Frink's arrival, there is a close-up of her mouthing "Come on," but we don't hear it, we only hear a giggle.
During the dream sequence, when Michele gets hit by Sandy Frink's limo, you hear Michele saying "Ow", but when you see a close up of Michele her mouth is not moving.
After their argument, while driving to the reunion, both Michele and Romy say "Fine," but Romy's mouth doesn't move.
The shadows of the camera and a crew member's hand can be seen on Romy when she and Michele are in the desert.
In the end of the movie where Romy and Michelle are lifting off in the helicopter, when they do an aerial shot of the class watching them lift off, you can see the shadow of the camera crew in a lift box.
After the reunion, Romy and Michele fly home together in Sandy's helicopter - abandoning the Jaguar that Romy went to so much trouble to get.
After graduation, Sandy became rich and famous, therefore his name and his invention would be all over the media. However, Heather, who was in love with Sandy for ages and cared about him, is completely clueless about his life and achievements, let alone about whether he is single or married.