Just read an interesting one today on a Gipsy Major last year. The pilot’s hand was injured by the prop while turning the prop to prime the engine(a requirement).
He had actually done a live mag check on the previous shutdown with no issue. Yet the ignition was intermittently live. Something to do with the earthing cap which is a different design from modern mags. A wire doesn’t always have to break for the mag to be live, just a single lack of continuity in the earthing circuit.
Just shows the importance of being paranoid even if the mag was just tested. Best to just make it a policy to always have the same level of paranoia when turning the prop.