I've noticed that some tab notation shows an unplayed string "sandwiched" in between played notes at the same point in time. For example, in Queen's "Tie Your Mother Down," there is a line that indicates the following: 3rd fret for low E, nothing for A string, open for D and G strings, 3rd fret for the B string, and nothing for the high E string. How do you not play the A string and still play the others? Thanks for any help.