- there's one "lead" player.  Important things about him:
    - he's the only one who gets the whip
    - he's the only one that enemies go for
    - when multiple people go on the spring jump, he always goes first
    - when you pull out a bomb, or whip, he's the only one who gets them, but he gets N copies
    - the view scrolls with the lead player only


- spring-traps only jump one player at a time



==== unintuitive ====

- when the "secondary" player picks something up that's held, the "primary" player is actually the one who ends
  up holding it

- when *either* player picks up something that's equipped (e.g. jetpack, parachute, ...), both
  characters get that ability

- when one person gets damaged, they all fall on the floor simultaneously