function killSomeone(person) {
    person.alive = false;
    console.log(person.fullName + " is killed.");

    // The magical line to catch the bad guy red handed!
    console.log(this);
}

var good_guy = {
    fullName: "The Good Guy",
    alive: true
};

var bad_guy = {
    fullName: "The Bad Guy",
    alive: true
};

// bad guy learns about killSomeone and borrows it.
bad_guy.killForFun = killSomeone;

bad_guy.killForFun(good_guy);