Calling down likely stack-offs

[TimM]

4BB is almost enough to play the hand normally, so you can't be sure he is stacking off here.

But if you are definitely going to showdown I'd want to get the money in as early in the hand as possible. I've seen short stacks save the last BB for another hand when they know there is no chance to win. No reason to give them the choice between saving a bet when they are lost and getting the money in when they have you beat.