I am now with you, especially with that last over before lunch yielding 15 runs. I suspect they may send Bairstow out after lunch with instructions to swing the bat at everything for a couple of overs (or until he's out), but I think they should declare and put Australia in immediately.
Tomorrow looks like a complete wash out at the moment and Sunday doesn't look much better. It's irrelevant if 189 is a big enough lead because if Australia exceed that total then it's almost certainly going to be a draw anyway. Got to hope for some brilliant bowling this afternoon and an Aussie collapse.
