Continuity mistake: In the scene where Anakin arrives on Mustafar and tells R2-D2 to stay with the ship, he pulls the hood of his robe over his head with two organic hands. His right hand should be mechanical. [This mistake is mentioned in the audio commentary: this shot is taken from a shot of Obi-Wan later in the film when leaving Padme's apartment. Still a mistake, though.] (01:32:55)
Trivia: General Grievous is permanently coughing when he talks. The cause is revealed in the last episode of the animated Emmy-winning TV series "Clone Wars." In that episode, Grievous kidnaps Palpatine and before leaving, is attacked by Mace Windu, who destroys part of his chest armour, making him cough for the first time.