It's exactly what it says on the tin. A powerful shout that scares the other bears (except for the zombears and ghouls) and causes the insanity to slowly creep into their minds! ...And probably the only noise they ever hear coming from Naughty when he's not growling or grunting. It's use is quite simple, with a press of R2 for PS3 or R trigger for the Xbox 360, Naughty will shout while waving his arms wildly and any bear in the hearing range will be scared. It's also useful for a sneak attack, scaring the bear instead of downright killing him. It's main purpose is to help pushing the bears into insanity, but the downside is that if overused, it loses it's efficency. In the Insanity! challenge intro video, it shows a random bear (usually the boss bear of that specific chapter) fainting on the spot after getting a boo! straight to the face, might just be a case of "cutscene superpower".
Naughty Bear[]
The Boo! is pretty much a loud shout that you use for scare the other bears. Let it be a loud shout in front of a group of bears or when you sneak behind them and shout instead of killing. It's useless against the zombies and the ghouls because of their extremely slow reflexes. It loses efficency if overused giving less and less points with each shout.
Naughty Bear: Panic In Paradise[]
The Boo! is present in this game too and plays exactly the same role. With the difference that now it's been massively expanded and got three different versions at our disposal. Plus, it consumes stamina and it can be "charged" if necessary.
Whispered Boo: Available from the start. Just tap R2 (PS3) or RT(Xbox 360) to have naughty whisper. It's a good way to lure unsuspecting bears in designed areas in a sneaky way. (Doesn't works on General Treacle)
Standard Boo: Available from the start. The classic Boo! that accompained us in the previous game as well. Same purpose, same efficency, only now it consumes stamina and once you'll run out, you will have to stay quiet, hidden in the foliage for a while.
Mega Boo: Unlocked at Level 20. The strongest of the trio! Hold down either R2 or RT for a few seconds and you'll be able to unleash this powerful roar. It scares a wider range of bears, but it consumes a lot of stamina.