var dog = {

    name: 'Killer',
    action: 'kills',

    getDescription: function() {
        return 'A ' + this.name + ' which ' + this.action;
    }

}

var dog1Description = dog.getDescription(); // get a traditional dog description

var boundGetDescription = dog.getDescription.bind({ name: 'Hound', action: 'tracks' }); // get a description with modified values for its 'this' value

var dog2Description = boundGetDescription();

var dog3Description =  dog.getDescription(); // get a traditional dog description

console.log(dog1Description); // A Killer which kills
console.log(dog2Description); // A Hound which tracks
console.log(dog3Description); // A Killer which kills