There were two such incidents. The first with Harry Daghlian stacking tungsten bricks around the "demon core" before dropping the final brick into place. The se

There were two such incidents. The first with Harry Daghlian stacking tungsten bricks around the "demon core" before dropping the final brick into place. The second with Louis Slotin and his infamous screwdriver. The whole idea of getting as close as possible to criticality with neutron reflectors was the part that was "tickling the dragon's tail". Not necessarily just the screwdriver method, which was particularly insane.