Spades Slick cannot return to being Hearts Boxcars because obviously Diamonds Droog is too busy being Clubs Deuce.
You just watched Trace throw a punch into thin air for some reason. That guy's awfully silly!
He then skulks off somewhere.
You don't realize he's following Droog's PAST TRAIL through the mansion until he gets to the point where it intersects with your trail, at which point he'll start following you.
But we all realized it. Because it's obvious and couldn't possibly be more clear.