Thank you for this, that's very helpful!

I think the Doctor's dual heartbeat would be sufficiently confusing that Scott wouldn't have a hope of telling whether he's lying. That's no problem at all!

And the Demon is likely to freak him out a bit, honestly. He will have no idea what he is and is likely to be wary at first. He might think he's something werewolf-related if he smells like dog though!