bart's trainer is doug sousse, he says not all bears are created equal. >> grizzlies would be the biggest concern. >> reporter: but sousse says if you do happen to come in contact with a bear there are a few things you should do. talk slow. move slower. >> slowly back away, increase the distance between you and the bear. absolutely never run under any conditions. >> reporter: if a bear charges protect yourself. >> if a bear were ever to be on top of you. what you would do to protect one's vital spots. cover your face and neck like this. >> reporter: with a little bear spray you can hopefully avoid position. defense. this would be in your holster. >> pull the safety off. just like that. >> yes. >> this is why you you. you will give one quick spray. perfect. perfect. often times that one quick spray will be enough to deter the bear. that would be great. so, just that pepper in their eyes, mucous membranes is often times enough. if it is not enough the bear keeps coming towards you. same posture like you did. unload the whole can. >> okay. wow. >> for "nightline" in yellowstone national park