Bloody Mackenzie's tomb — I came out of Greyfriars with marks I can't explain

Did one of the City of the Dead tours in Edinburgh a few years back, the one that takes you into the Covenanters' Prison at the back of Greyfriars. Background for them that don't know: George Mackenzie was Lord Advocate around 1679, the man who locked up something like a thousand Covenanters in that……