Revealing mistake: During Kenobi's final lightsaber battle with Vader, Kenobi tips his lightsaber downwards, right before a scene change. The white "glow" that should be there isn't, showing the stick-like prop the actors used in filming. There is a small white light at the tip, too. This was not fixed in the Special Edition, but it was finally fixed on the 2004 DVD. (01:31:25)
Continuity mistake: When Luke and Obi Wan arrive at the Cantina, watch the Jawas sitting outside the Cantina. They're initially sitting in a shadow, but when Luke and Obi-Wan walk towards them, they're suddenly in broad daylight. (00:42:45)
Continuity mistake: When Luke comes to eat dinner with his aunt and uncle, as the shot ends, he has just sat down by the table, but in the next shot, he's already helping himself to the food. (00:22:45)
Continuity mistake: There's only grayish objects in the garbage compactor but while Luke and Han are removing their uniform, many orange objects appears in it. (01:22:10)
Continuity mistake: When Vader picks up the rebel in a choke grip, the legs of the stormtrooper in the doorway behind them are apart. In the shot of the rebel's feet, the trooper's legs are together. When Vader tosses the dead rebel into the wall, the trooper's legs are apart again.
Continuity mistake: When Luke and his aunt and uncle are eating at the table, the white drink pitcher alternates from being next to Luke's cup to being across the table throughout the scene.
Continuity mistake: When Aunt Beru speaks to Luke about buying droids, there are many shrubs besides Luke. In the next shot, they are gone.
Deliberate mistake: When Obi Wan deactivates the Death Star's force field, there's an electronic gauge going down and a sign in clear English with the word POWER - as we've seen in shuttles and other places, they don't use English. The studio decided it was better to show "power" and "tractor beam" in English so that the audience would know what Obi-Wan was doing. The lettering we see in Jedi doesn't really affect the plot, so it doesn't need to be English. Still doesn't really fit though. This is fixed on the DVD.
Continuity mistake: Special Edition: When Han is talking to Jabba the Hutt, as Jabba says, "Why did you fry poor Greedo?", the man standing to his left is pointing a blaster towards Han. In the next shot, the man is no longer pointing the blaster at him. (00:51:00)
Other mistake: After the escape from the Death Star, the first TIE apparently blows up, but behind the explosion we can see it still intact.
Deliberate mistake: On Tatooine, after C-3PO tells R2, "No more adventures," he walks off in the opposite direction. When C-3PO reaches the skeletal remains in the sand, and complains that the malfunctioning little twerp tricked him, the closeups of 3PO are flipped shots (also note the position/direction of the skeletal head). (00:10:50)
Trivia: When they power-up the Death Star, the control panel is a Grass Valley switcher, production equipment which is still prevalent in television stations everywhere.
Continuity mistake: In the control room when Obi Wan decides to leave them, the red beam on the radar behind him points down. When it cuts it is suddenly pointing up. It couldn't have moved that fast.
Revealing mistake: When the droids head towards Tatooine in their escape pod, a rotating imperial ship is shown in the pod's window, getting smaller as the pod moves away. Regrettably, the star field gets smaller at the same rate as the ship, something that would only happen if you were moving away from a photograph, painting etc. (00:06:55)
Continuity mistake: When Luke is outside of the farm seaching for R2D2 with his binoculars, C3PO is not visible in them even when Luke turns in front of him.
Other mistake: After the tractor beam pulls the Millennium Falcon into the Death Star, there's a shot of a MSE-6 droid ("mouse droid") at the feet of four stormtroopers. The trooper in the back right, is holding onto his helmet in a desperate attempt to keep it from falling off. (01:03:15)
Continuity mistake: When R2D2 has finished showing Leia's holo-message to Luke, C3P0 says something like "he has become a bit eccentric." When he says that, there is a wire coming from his belly. It was not there before or after.
Revealing mistake: In the trash compactor, after C-3PO realises that he turned off the comlink, Leia grabs the bar used to stop the compactor and her hand sinks in and puts a dent in the bar. When she loosens her grip, it returns to normal. No wonder it was useless at bracing the walls...
Continuity mistake: When R2 and 3PO are walking in the desert look at the sun's reflection on C-3PO's head throughout the shots. It keeps changing places.
Continuity mistake: As R2-D2 is rolling through the canyon, he's on a smooth part of the land. He then stops and looks around. When he starts moving again, the terrain has changed and is now full of rocks and pebbles. (00:11:20)
Answer: Presumably because the monster has pulled him through the lair of whatever they are standing on into whatever space the rest of the body of the monster lives in. Obviously, the monster doesn't live in the part of the part of the compactor that does the compacting or it would be already compacted.
Myridon