Given a few scenarios, he had to propose a suitable punishment. According to him, an incompetent builder should be shot by a crossbow, a nagging wife should be hanged, and truth can be determined by killing both parties.
(Bloodthirsty as he sounds, the actual code is just as severe. He'd just banish a nun for going into a tavern, instead of burning her, and a boy who slapped his father would be spanked, rather than having both hands cut off.)
After I stopped laughing (and vowed never to nag my husband), I asked him about other crimes. Apparently if you steal a trampoline you should go to jail for a year, but if you break into a house it should be for life. You'd also get life for kidnapping his sister, but it'd be life tied to a tree, rather than in jail.
Then I asked him what he thought the worst crime was.
"Are some murders worse than others?"
He contemplated that for a while, then shrugged.
"Is it worse or the same to murder a baby or a 90-year-old?"
"It's worse to kill a baby."
"Because they don't get to grow up."
"What about rich and poor people - is it worse or the same?"
"It's worse to murder rich people."
"Because they're important, usually. In medieval times, anyway."
"What about now?"
"It's still worse to murder rich people. Murdering a rich baby is the worst thing you can do."
"Are we rich?"
"So if someone murdered (one of his twin siblings), it wouldn't be as bad as murdering a rich three-year-old?"
"Hmm." That made him think. "Actually, it's the same."
It was interesting to discover his values, and to challenge him on them. I'm really proud of him.
His siblings listened with interest, so I asked them, too. "What's the worst thing you can do? The naughtiest thing?" Naturally their answers reflected some recent events.
Vieve's answer was "Splash water on the floor", our latest bathtime battle.
Finn was still traumatised by a recent run-in with a two-year-old. "Wet me at Playcentre with a hose."
"And what's the best thing you can do? The most good?"
Finn thought it was to "jump on the trampoline."
Vieve's answer made me laugh and laugh. "Stay in your bed and not get out."
HECK yes, that's the best thing you can do in our house!
Ask your kids: what's the worst thing you can do? What should be the punishment? I'd love to see what they say.