Continuity mistake: As Gunter is crying in the dorm, the number of bananas change between shots as well as the position of them on the floor. The changes are most notable when Fry approaches Gunter in the room.
Continuity mistake: Whilst Fry, Leela and the professor are on the log near the waterfall they are very close to the right side of the river. A few shots after Gunter puts the hat back on his head you can see they and the log are now all the way over to the left side of the river.
Deliberate mistake: In the dorm room, Fry's punch cup appears out of nowhere. [According to the DVD commentary, this was done on purpose.]
Continuity mistake: In the scene where Fry and the professor is trying to make Gunter choose between the banana and the hat, the distance between Fry, the professor, and Leela changes noticeably between shots. First Fry and the professor are wide apart with Leela behind Fry. Then after Leela hears the robot-house's boat approaching, they're all suddenly down by the lake standing next to each other.
Continuity mistake: When Gunter is trying to figure out where the hat goes, the banana disappears and reappears between shots. When Gunter finally figures out the hat goes on the head the banana is nowhere to be seen, yet when he needs it to do some calculations the banana is on the ground right next to him.
Answer: The initial number is 0101100101 = 357. When reflected in a mirror, however, it reads 1010011010 = 666 (the number of the Beast). It is a parody of The Shining, where the words Red Rum are seen as the word murder in the mirror.
Sierra1 ★