The last two dogs my dad had were a pair of black labs. They had two different kinds of barks. If you were woken up in the middle of the night with the first kind of bark you could just roll over and go back to sleep because it was a "I heard something but not sure what it is" bark. The second bark was the kind where you had to get out of bed grab a flashlight and go take a look. You would always find some wild animal in the yard or and escaped farm animal or something else amiss. The barks were very different from each other.