Leo and Charlie had been watching a film about Doctor Frankenstein. They were convinced that a corpse could be revived by applying electricity to the nerve endings. After all, Charlie had some recollection of seeing a dead frog's legs begin to twitch again when electrified.
They found an unfortunate cat lying by the roadside. It had been hit by a car but apart from being dead, it seemed undamaged.
They took it to Leo's shed and wired it up to the mains. Electricity couldn't revive a corpse, but as Leo slumped to the ground, they found it could create one.