Beating the enemy

Yosef already says yes to burying Yaakov in Me'aras HaMachpeilah, and he has the power to do it. Yaakov still makes him swear. Later, when Pharaoh looks for a way out of that oath, Yosef answers him with a line that sounds almost like a threat to the king.Why would Yosef speak that way, and what did Pharaoh understand that stopped him? The Steipler, working from a Gemara in Sotah, explains what was really at stake. A soldier, a night alarm and an unfinished shoelace bring it to its sharpest point.