A newbee hunter asked a experienced old hunter how to hunt bears. The old man answered:" It is easy, my son. I've hunted hundreds of bears in my life. You just need to grab your gun and take a ride to some mountains nearby. First, find a cave or stone cavern that might shelter a bear. Second, make some 'Woo! Woo!' sound so that the bear inside would mistake it as a signal of its companion. It should also make the same sound back at you. After it comes out, you just pull the trigger. Easy, right?" The newbee nodded and exited without coming back for months. After a long time, the old hunter saw that newbee on a street and found him crippled, with an ear lost and an eye blind. He asked him what happened. The newbee says: "I did as what you told me before. But god darn it, when something inside that cavern answered my 'Woo! Woo!', I didn't expect a train would come out and hit me!"