I'm inclined to think they'll do the transporting liquid one or something in pairs like BB15, but then I realized there's no way they'll have time to show that, strategy leading up to nominations, the nomination ceremony, AND the battle of the block on Sunday's episode.
Allison Grodner shed some light on the confusing twist:
"They [the HOHs] are ultimately going head to head in this competition with Battle of the Block, where one is going to end up in power and one is going to end up not in power."
Looks like everyone was partially right - but it's not the nominees facing off. I feel that having the nominees facing off is better... they have way more to lose than the HOH does!
