Frenzy

Frenzy - The Beast (in V:tM)

In V:TM, frenzy is when the Beast takes over the vampire's personality, usually a result of extreme stress such as starvation or public humiliation. The player may choose to resist frenzy (with a Self-Control roll) or enter the frenzy but attempt to guide the character's actions with Instinct rolls. The player may spend a point of Willpower to put the frenzy on hold for one round. Character in frenzy are immune to Rötschreck.

SOURCE: Vampire: the Masquerade @ Wiki

Causes of Frenzy (in V:B's)

Hunger can induce Frenzy, as can the fear and anger caused by taking physical damage. The risk of Frenzy relates directly to your Humanity. A vampire in touch with their former humanity can keep the Beast at bay; a craven undead killer will succumb more frequently. This risk is compounded by hunger. Feed often and maintain your Humanity to prevent Frenzy.

SOURCE: Vampire: Bloodlines @ GameBanshee