Attempting to pick a lock with a credit card may result in it slipping through the crack (ending up either inside the box or on the other side of the door). The chance for this is getting a 1 on a rnd(Dex*2) roll (with an uncursed card; cursed cards will always slip through and blessed ones will never slip through). If fumbling, use Dex/4 instead of Dex*2.