to find out, we have robin bennett and susan briggs. they call themselves the dog gurus. they're also the authors of the book "off-leash dog play." welcome. >> thanks. we're happy to be here. >> it's great to be here with you today. >> so, susan, we can't assume that a wagging tail is always a good sign, can we? >> no, you can't. we love our dogs, and they communicate a lot to us, and the tail is an important part of that, but just because it's wagging its tail doesn't mean it's friendly and you should approach it. >> do you have to worry about speed or where they're holding their tail? >> yes. you look at what position is the tail, whether they're holding it high or low, and you look at how fast that wag is. >> robin, can you give us some specific examples? >> well, sure. let's say you're going to pet that dog, and he ends up turning mean. you might have noticed the dog's tail was wagging, but he might have been protecting his owner. so that tail wag might have been way up over his back, really high, because that's a really good sign that the dog is protecting something,