The girls in the light house seem like logical, level-headed individuals at first. Once they find out someone tried to poison the food they freak out.
You'd Expect: At least one of them to take charge and rationally reason who did it.
Instead: Each of them proceeds to freak out and spray bullets everywhere. Bonus points in the film since once everyone is dead one of the girls asks the real murderer if she did it and the girl shakes her head no. The whole thing would've been solved if she trusted the word of her classmates like she did then.
Mitsuko has a moment in the manga when she tries to seduce Kiriyama of all people.
You'd Expect: Before the game Mitsuko determined which guys seemed easy to seduce. Apparently, Kiriyama's Dull Eyes of Unhappiness and expressionless face weren't a big enough clue.
Instead: She goes along with the plan and ends up failing by exposing herself out in the open.
Hirono also gets one in the film. She holds Mitsuko at gunpoint while the latter has no gun.
You'd Expect: Hirono kills Mitsuko quickly since she knows how dangerous she is.
Instead: She kicks her while her down and spends so much time doing so she ends up getting zapped by Mitsuko's stunner and ends up with her gun stolen.
Toshinori Oda in all versions receives a bulletproof vest, and is gunned down by Kiriyama but survives.
You'd Expect: He'd play possum and wait for Kiriyama to move along (and, to be fair, he DOES do this in the novel but Kiriyama goes back for a Double Tap).
Instead: In the film, after Kiriyama leaves, Toshinori actually shouts out "I survived thanks to my awesome bulletproof vest!"...at which point Kiriyama returns and beheads him with a sword. In the manga, he fakes a death rattle in the hopes that Kiriyama would approach to check on him, at which point he'd shoot Kiriyama. When Toshinori springs to life, Kiriyama quickly jumps between Toshinori's legs and fires a volley of bullets into his unguarded dick.