Continuity mistake: On Tatooine, after Anakin's mother died, and they laid her to rest, you notice the shadows of the tombstone's are all facing one direction. When R2-D2 comes over, you'll notice that his shadow is going in a different direction. Can't be explained by the two suns, as we've seen many times that they don't produce two distinct shadows. (01:27:45)
Continuity mistake: In the scene where Obi-Wan lands on the cloners' planet. Rain drops go from right to left as he walk to the door. In the next 180 degree scene change as he enters the building they are still going right to left. (00:41:35)
Revealing mistake: When Anakin is talking to Palpatine, the shot pans to the door, and it is obvious that the door and the furniture are painted. (00:26:15)
Continuity mistake: Yoda drops his cane to fight Count Dooku. Then in the wide shots, the cane (CG animated) is no longer on the floor (anywhere), until Yoda conveniently needs it again and pulls it into his hand from nowhere. (02:02:25)
Chosen answer: Because he dropped it earlier while chasing Zam Wesell on Coruscant. Obi-Wan caught it that time and scolded him for losing it.
Sierra1 ★