Elementary

B. has a science degree -- more than one, actually -- which sometimes gives rise to a certain amount of discussion when we watch science fiction or similar on the television.

'All irregularities will be handled by the forces controlling each dimension,' the TV informed us the other day. 'Transuranic heavy elements may not be used where there is life. Medium atomic weights are available: Gold, Copper, Lead, Jet, Diamond, Radium, Sapphire, Silver and Steel. Sapphire and Steel have been assigned.'

Fortunately we managed to get past the whole 'But Sapphire and Steel aren't elements!' conversation a while ago, agreeing that they might be considered elements in some alchemical sense which diverges from the paradigm used by modern chemistry. This time, however, B. suddenly said, 'But Jet and Diamond are forms of Carbon. That's got an atomic weight of 12. 12 isn't medium!'

I thought about this for a moment. 'Perhaps there are an awful lot of lighter agents, though. Maybe they have a whole load of them based around various allotropes of Hydrogen and Helium, for working inside suns.'

She looked at me suspiciously. 'I suppose that's a technobabble workaround for the scriptwriter's error, yes.'

I'm getting good at those.