Scenario: The party encounters large skeletons. The combat map has a lot of squares marked as (possibly) bottomless pits. Each skeleton takes up four squares. If they are forced towards the edge, how many of their squares must be on pit squares before they can fall (i.e. gets a saving throw to avoid falling)?
1 square (i.e. a corner of their space)? 2 squares (i.e. half their space)?