AC/DC - "Thunderstruck"

A lot of AC/DC's hooks are single string riffs where Angus Young (guitars) alternates between freted notes and playing the open string. Like "Thunderstruck" for example.
The famous intro/main theme for the song came from a warmup guitar exercise he learned for stretching his fingers. Angus Young : "I was just fiddling around with my left hand when I came up with that riff. I played it more by accident than anything. I thought 'not bad' and put it on tape". Sounds so easy...
When recording that part of the song, all of the other strings were taken off his guitar except for the B string (second thinnest) so that no accidental notes would be hit.
Available on the album "The Razor's Edge"