Revealing mistake: Sand people are up on a hill overlooking a valley below where Luke is passing by in his speeder. One of the sand people takes aim at Luke, but his companion stops him. Right before the end of the shot, as the speeder is traveling towards the lower right corner of the screen, it becomes transparent. This is a multiple exposure shot, and the path of the speeder wasn't quite lined-up right. (00:27:55)
Revealing mistake: When the Tusken Raiders are seen raiding Luke's speeder, you can actually see the wheels or at least whatever is holding it up off the ground. (00:28:10)
Continuity mistake: When Luke has been knocked unconscious by the Sand People and Obi-Wan appears and scares them off, there's a shot of Luke lying there and one of his sleeves is in disarray, halfway up his arm. But when Obi-Wan checks his pulse, he does it right through a fully-covered-by-the-sleeve wrist. (00:28:25)
Deliberate mistake: After the Tusken Raider has attacked Luke, he raises his stick over his head and shouts. The movement of his clothing is extremely unnatural. During the editing, they put the same footage forward, then backward many times, to add emphasis to his movements, but it looks decidedly odd. (00:29:02)
Continuity mistake: After Obi-wan saves Luke from the sand people, there is a shot of him sitting on a rock and his white robe is visible, then there is a close-up and he says "I don't seem to remember owning a droid" and his robe is not visible. (00:30:20)
Continuity mistake: When Luke is in Obi-Wan's house trying Anakin's lightsaber, the coat behind him keeps appearing and disappearing. (00:32:15)
Continuity mistake: When Obi-wan and Luke are watching the hologram of Princess Leia projected onto a small table, the objects on the table change position and number in each shot. (00:33:35)
Revealing mistake: When Luke first ignites his lightsaber, he turns it from the right side of the screen to the left side. When the blade is facing the screen, the lightsaber appears flatter than in the previous shot. (00:33:50)
Revealing mistake: When Luke ignites his new lightsaber in Ben's house, the reflection of the stick used during the filming is visible on C-3PO's body. (00:33:55)
Continuity mistake: When Luke is in Obi-Wan's home, C-3PO tells him "Sir, if you'll not be needing me, I'll close down for a while." and Luke nods. However, when R2-D2 projects Leia's recording, C-3PO turns his head to look at it. (This is only just visible). (00:35:06)
Continuity mistake: Special Edition: Luke, accompanied by the droids and Obi Wan, is in the speeder heading into Mos Eisley, but just as the shot ends it looks like they're about to run over a few pedestrians... they're heading full speed at a group of three or four people just when the camera angle changes. (00:40:50)
Revealing mistake: You can see the arm of the crane used to lower the torture device through the door when it is going into Leia's room. (00:41:15)
Revealing mistake: In the scene where the "torture" robot goes to get information from the princess, if you look carefully on the side of the syringe you will read "monoject", which is an American hypodermic syringe manufacturer. (00:41:30)
Revealing mistake: When C3PO is carrying a dead Jawa to the funeral pyre, it looks like it doesn't have a head, legs and arms. It's like a costume stuffed with a pillow. (00:41:45)
Continuity mistake: Special Edition DVD. When Luke, Obi-Wan and droids arrive at space bar in Mos Eisley, notice the herder with white jacket followed by a dinosaur-creature on a leash and then the R2 unit. In the next shot the dinosaur and R2 are there, but the herder has disappeared. (00:42:20)
Continuity mistake: When we see Ben, Luke, R2-D2 and C-3PO on the cliff looking at Mos Eisley Spaceport, you can see Luke's speeder behind the two droids, but when we see a close-up of the four characters, the speeder is nowhere to be seen. (00:42:30)
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: In the cantina, the alien who eventually gets his arm cut off is hassling Luke. In one shot he puts his hand on Luke's shoulder, but in the next his hand's nowhere in sight. (00:44:40)
Continuity mistake: When a confrontional alien thug threatens Luke and Ben interferes, the thug has his hand on Luke's upper arm. In the next shot, his hand is on Luke's shoulder. (00:45:00)
Continuity mistake: In the Cantina, the burly alien threatening Luke pulls out his blaster twice, once in the background when Luke crashes into the table, and once as Ben's lightsaber is heard being ignited. (00:45:05)
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