Methinks our esteemed guest Some Bloke has hit it right:

> You know you’re singing trad when one half of the room
> reckons you’ve got it wrong and the other half were
> hoping you’d sing something they’ve heard of ....

.... though my version, from recent experience, is: if half the room starts singing along to the first chorus, and the youngsters are joining in by the third one. It's disconcerting if the oldsters are concentrated on one side. (For the record, it was Pleasant and Delightful --- as was the response.)

I'm slightly worried, though, that I first read our esteemed guest's first line as:

> Wow. Little altars here on Mudcat eh?