Upon deciding to make up a new song rather than do a cover, Sir Paul said he turned up to the recording session with a "crazy guitar" actor Johnny Depp had given him.

BBC: Sir Paul McCartney surprised at 17th Grammy win

Both times I've tried "Crazy Train" on pro expert guitar, I've had such a visceral feel for what I was playing, It challenged me to play more precisely than I could ever on my own, and the sense of accomplishment was equivalently fulfilling.

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