When Fozzie gets Kermit's "Dragonfly Ripple" cone from the ice cream man, it's a shade of bright lime green. When he gives it to Kermit, it's gray. After the group spots Gonzo floating with the balloons the cone is green again, but a different shade.
Just as the gang hits the billboard for the pie advertisement, Fozzie yells, and the steering wheel comes off, but it's reattached the next time we see them in the Woodie.
When Kermit and friends first enter the front office of Lew Lord and speak to the secretary, the fan is already turned on in the background. However, Kermit then turns the fan on from the off position to spread the animal dander.
When Fozzie stops the car the first time to speak to Big Bird the car is further up; when the camera moves to Big Bird, he is seen standing directly next to the car.
Fozzie's Studebaker has a cracked windshield in several shots, but not in others during "Moving Right Along".
While Kermit is waiting for Miss Piggy to come back from the phone, time passes as indicated by the position of the moon rising in the background. The position of the stars should also change with the passage of time.
When Kermit goes into the El Sleezo Café, he leaves his banjo outside. He is not seen to retrieve it before getting into the Studebaker with Fozzie, but he somehow reacquires it when he plays and sings "Movin' Right Along" with Fozzie. The banjo can in fact be seen in his lap just before Fozzie drives away from the cafe, it's just difficult to see.
As the movie begins, the planet Earth on top of the World Wide Studios entrance is actually spinning backwards. It is only a statue and thus does not have to be a completely accurate representation of the Earth. Alternately, as it is meant to be a parody of the Universal Studios logo, this may have been deliberate.
When Gonzo is flying with the balloons and says "Look at our little car down there", the sunlight makes the cord suspending the balloons visible.
The back of the theater seat Animal is sitting in clearly shows an exact outline of the chunk Animal rips off when he eventually starts eating the seat.
When Kermit is riding his bike down the street toward the beginning of the movie, two strings can be seen momentarily in front and behind the bike.
After the Miss Bogen County Beauty Pageant emcee announces Debbie-Sue Anderson as the first runner-up, she is clearly seen wearing a third place sash as the audience applauds.
When Fozzie and Kermit are looking at the map, before they run off the road at the church, the road in the background makes two turns, but the steering wheel stays in basically the same position.
During Kermit and Piggy's dinner date, the lamp behind and to their right is on, but as the waiter comes in, it turns off. It comes back on when he slams the $.95 wine down on the table.
At the start of "The Magic Store" number, Robin is sitting next to Scooter on the train filled with movie props. He is seen again in the background a few moments later when Miss Piggy calls for make-up. Prior to this, Robin was only seen in the framing sequences watching the movie in a theater, not in the movie itself.
When Gonzo is flying over the countryside with the balloons, his mouth never moves during any of his lines except in the close-up shot, when he says "Ah, this is the place to be. Whoopeeeeee!"
Immediately after Kermit and Fozzie's first encounter with Doc Hopper, as Fozzie is driving away, Doc Hopper speaks a couple of lines ("Hey, that's my Caddy!" and "Frog, it's money we're talking about!"), but his mouth does not move.
At the end of "I'm Going to Go Back There Someday", when Kermit leaves the group momentarily, Rowlf stops playing the harmonica for a few seconds, but we continue to hear the solo harmonica line.
Just before the film malfunctions, the motion slowly stops, but the background music keeps going at its normal pace until the film breaks.
At the end of "I Hope That Somethin' Better Comes Along", when
Kermit and Rowlf harmonize on a final pair of long notes, they both hold the notes, audibly, until the end of the song, but Rowlf's mouth changes to a scat/improv line that he sings and we hear. (In other words, his voice is heard on two different musical lines at the same time).
When Miss Piggy jumps off the balcony to attack the men and save Kermit, an arm covered by a long black glove is seen throwing her.
We can see a sliver of Jim Henson's hair moving Kermit from behind a crate, after the owner is thrown out of El Sleezo Cafe.
When the freshly-painted Studebaker drives off and the Electric Mayhem band is waving goodbye, look closely at the bottom of Zoot. We can see the puppeteer's forearm quite clearly.
It is obvious that much of the outdoor scenes were filmed in southern California even though the movie takes place in many states.
When the gang see and pull into Mad Man Mooney's, you can see the street sign for San Fernando Rd, which is a street only in Glendale and Burbank, California, but by this point they're supposed to be somewhere in the Midwest or the shallow south, nowhere near the west coast yet.