Sucking out brains

Jummy, brains! When one of your min defeats an enemy, it becomes prone, allowing any flayer to enslave, slay or devour the target's brain. I've also bumped creature life so fights take a bit longer than a single strike.

Right now the only desirable options are enslave or devour, as devour heals a wounded flayer, and there is no penalty for enslaving. We will mend this in the future, when the player will have to balance thrall against resources and available flayers.