public Animal peekAny() {
        if (noAnimal()) {
            throw new IllegalStateException("No animals!");
        } else if (noDog()) {
            return peekCat();
        } else if (noCat()) {
            return peekDog();
        } else if (peekDog().timestamp < peekCat().timestamp) {
            return peekDog();
        } else {
            return peekCat();
        }
    }