I analyzed the particular duel between Anakin and Count Dooku, and if you see how Anakin tried to re-engage Dooku seconds before his arm was severed, you see that Anakin tried to be honorable and salute Dooku...but the Count slashed Anakin's outstretched arm. It is obvious Dooku did this because Anakin was a little more formidable than Dooku anticipated. (he is panting and clearly startled at Anakin's prowess).
Originally posted by finti
Vader vs Luke in ESB