When Round 3 is announced, The Voice says whoever has killed the most people lives, but never says that ties aren't allowed. This retroactively makes the entire experiment a prisoner dilemma, because if everyone had cooperated and refused to kill, 20 people would have been "tied" with 0 kills, and everyone would have a 25% chance of survival, instead of the measly 1.25% they ended up with. That said, each person can always increase their chances of survival by killing, in classic Prisoner's Dilemma fashion.
There's technically an even better way to game the system through cooperation, but it would have required advanced foreknowledge of Round 3. If 40 people each killed one person, they'd all be tied with one kill, without 60 deaths in round 2, giving everyone a 50/50 shot.
Then again, with what the ending shot - other "winners" exiting Belko buildings and "Stage One" ending - reveals, it's highly unlikely the Voice would have allowed such loopholes to be implemented, and would have demanded more deaths until there was only one person left.
And this is only this game's version of Round 3. Had 30 people been killed in the required time, who knows what the next round would have been with 50 people left.
The brain bombs look like ball bearings, but that ensures that they can be transported inconspicuously.
The workers who are left at the end of the ultimatum-mass kill are mostly all lead characters, kills to their name, and those without significant injury. What's brilliant about this is, as a film we still have characters we can identify easily; but as the experiment, the Voice has kept on people who are either willing to kill, have shown attempts at adverting the game, and those who can still physically play. So they used the mass kill to eliminate the fodder so they can continue whatever study they're doing with the widest range of variables, and ultimately keep things interesting.
They also kept people with relationships to each other. There were many people in the basement tunnel, but the one who had a kill and his secretary were the only ones to not have their heads blown.
I know this isn't the kind of movie where I should question, but did these people really spend billions of dollars just to find out whether or not people would kill each other if you threaten to blow up their heads if they don't?
Scientists have done worse in real life.
The Nazi experiments were insanely unnecessary, yielded no significant results, and resulted in a horrible amount of deaths. With that said, things such as the Stanford Prison Experiment is similar when exploring how far the human psyche can be pushed when given some measure of power. Or Thomas Edison electrocuting multiple animals just to see how electricity affected them, not humans but still horrific. While Henrietta Lacks' cells were useful to scientific advancement, it was still unbelievably immoral. The fact is, this isn't that far fetched.
The game only truly ends when "Stage Two" starts. This is after Mike has killed his "Voice". Does this mean that all of "The Voices" in all the other Belko buildings shown have their own "Voice"; who was gaming them as much as "The Voices" were gaming their original test subjects?
