I think the "argument" with Zack was all part of "The Plan" that no one could remember. Apparently, it was set up for Dave to be the one that was supposed to choose, but I think Kavita figured that out and picked Scott instead. You may have noticed she kissed Dave on the cheek as she went by (at least I think she did). Perhaps there was a little sympathy for the devil there?
Toni made a good move by making the "pact" with Scott.