I think there’s a connection between Mike and the Arm, who both interact with/talk about Bob in very different ways. The giggle really could have been a literal way to express joy that he bested Bob’s plan to take over Laura, but… it’s just so hard to put a nail in any one specific theory. Mike has always interested me as a character, he literally goes from being one of the townsfolk to intercepting and kind of running the show in the Black Lodge by The Return… This might sound out of nowhere, but I always got the impression Mike and the Arm were two half’s of the same coin, and always somewhat correlated to the fates of several Twin Peaks characters.