tonight on "nightline," angels and demons. they may look like normal teens, shopping, riding, doing karate. bull they claim they are battling exorcists. meet the teenage trio claiming to be satan's worst nightmare. fat camp. when fido looks flabby, would you send your dog to a fitness camp? the new industry battling pet obesity. is it vanity or should you be worried about your best friend? and hello dolly. she's everybody's favorite nine to fiver. the queen of country music.

tonight, dolly parton opens up about how she felt about whitney houston and the famous song they both share. ♪ i will always love you >> announcer: from the global resources of abc news, with terry moran, cynthia mcfadden and bill weir in new york city, this is "nightline," april 5th, 2012. >> good evening, i'm bill weir. for many, the devil made me do it is a bumper sticker punch line or old flip wilson routine. but according to the three young women you're about to meet, satan is real and at least one member of his demon army might be living inside you tonight. the gospels tell of jesus casting evil spirits out of helpless victims and these teenagers say they can do the same. but are they driven by faith oral fame? here's abc's dan harris. >> reporter: they are black belts in karate.

they are ace horseback riders. and they are also demon fight earls. the leader of the pack, brynne. they call her the enforcer. she's 17, home school and a regular on the beauty pageant circuit. then, there's savannah, the compassionate one. she's 20, a college student and she looks likes to shop. and tess, the middleman. she can do both good cop and bad cop. she's 17 and performs in musicals. what do you say to people who just don't believe this stuff at all? >> they should come and watch what we do. >> who told you to come? >> satan! >> after seeing an actual exorcism by us, you will walk away with no doubt whatsoever. there is a war going on every day, being waged against us. satan hates us. we know where the enemy is. we know what he's attacking and we can fight back. >> get your hands off me! >> reporter: their teacher is brynne's father, bob larson, who

says he's performed over 15,000 exorcisms. and claims demons are much more common than many people think. >> i know it sounds controversial but maybe half the population. >> reporter: half? >> half. >> reporter: of the world? >> yes. >> reporter: so it's possible that i could have a demon inside me and not know it? >> yes. >> reporter: before every exorcism, larson and the girls do a briefing here at the office they use in phoenix, arizona. >> remember, you are exorcists. so, we have to get those demons. >> reporter: and then it begins. >> what is your name? answer us! >> reporter: this woman's name is gina. it's her first exorcism. the girls, armed with crosses, bibles and holy water, soummon the demon within her and the demon apparently takes over gina's body and speaks. >> i will not! >> reporter: how do you actually know if somebody is demonically possessed? >> usually when you look in their eyes, you can see that evil staring back at you.

when a demon comes into one, its desire is to kill stroi that person's life. >> who are you? >> reporter: as the girls explain it, there are many different types of demons. >> there's hate, murder, anger. all of those are very violent demons. >> reporter: look at what happens at the climax of gina's exorcism. it takes four men to hold her back. this can be dangerous work. >> the christian life is risky. taking on the devil is risky. but what's riskier? saying no to god? saying no to god, the devil's got you. >> reporter: not withstanding their exorcism thing, the girls are, in many ways, quite normal and likable. >> we're not very threatening. >> not threatening, yeah. >> reporter: they are even afraid of bugs. you are scared of a bugened you fight -- >> bugs aren't afraid of crosses. >> she's mine. >> no, she's not. she's a child of god. >> reporter: but there are some very serious questions about the safety and the morality of what these girls are doing for

people. >> smitten by the sword of the spirit? >> reporter: how do you know that the people you're seeing aren't simply mentally ill? >> we find out as much about them as possible. are they under care of a psychologist or a -- >> in some cases, we can't help them, we have to turn them over to therapy or professional help. but sometimes it is just demons. >> reporter: we met this grandmother named sandy, who flew in from dallas for an exorcism. she says she has demons. >> they talk to me. >> reporter: they talk to you? >> oh, yes. and they have hurt me. they've hurt me, physically. i have welts on my legs where they have held me down and raped me. >> reporter: raped you? the demon? >> yes. >> reporter: although she commits she has sought the help of a psychologist in the past, she says therapy was not helpful. but even with 30 years of experience, are bob and his girls really qualified to help

people? you are not a trained mental health expert. >> no. >> reporter: so it's possible, it seems to me, that you are performing exorcisms on people who actually need medication, talk therapy, perhaps even hospitalization and can't that be a dangerous thing for the people are you trying to treat? >> if you have a demon that is blocking the therapeutic help, the therapy's not going to go anywhere significantly. >> reporter: but larson, already a veteran of one fled reality show, definitely has critics. what are the worst thing people say you? >> i pray on weak minds, weak-willed individuals. and, of course, what i do is sensational. >> reporter: any truth to niece of those charges? >> jesus performed an exorcism on a naked man in a cemetery. in the bible. that's pretty sensational. i haven't done that yet. >> reporter: what's more, these sessions are not free.

and larson insists one session alone almost never does the trick. what does hi charge? >> his suggested rate is 400 and something. >> reporter: it's worth it? >> to get the demons out of me? i would pay anything. >> reporter: the argument, i would imagine, this guy is taking money from people who need help and he's charging the money to perform these bogus -- >> wait a minute. you are paid. handsomely. so is anybody who has a responsible position in the public eye. and we have to fund what we do. >> reporter: whatever you think of what bob larson and his young proteges are doing -- >> in the name of the father, son and holy spirit. >> no, no. >> reporter: we may be about to see much more of them. larson says he's currently weighing sefrm offers for new reality shows starring the girls. >> the power is broken. >> reporter: for "nightline," this is dan harris in phoenix. >> thank, dan. coming up, the other obesity

epidemic in america. and a fat camp for dogs. ♪[music plays] ♪[music plays] ♪[music plays]

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>> announcer: "nightline" continues from new york city with bill weir. >> in recent years, the american medical community has wrestled with the assumption that a staggering 35% of the people in this country are obese. but a new study published this week makes the case if we modify the body mass measurement, it's col closer to 60%. even our pets are now bulging symbols of this land of plenty where loving helping of of table scraps have led to a new sobbering industry. doggy fat camps. here's abc's john berman. >> reporter: so charming but so

chubby. sol aw, gee, adorable, but so oh, gosh, obese. so furry, so friendly, but so fat. ten dogs at month long doggy fat camp. who will be the biggest loser? will it be chase, a 90-pound black lab? >> i try not to overfeed him but he tends to eat everything i eat. >> reporter: will it be sugar and possum? >> 46.6. >> reporter: how much does sugar need to lose? >> she needs to be at 30 pounds. >> oh, my goodness. >> reporter: could it be lucky, the 84-pound lab mix? how long has lucky been hefty? >> about three years. >> reporter: so, a lot? >> yes. >> reporter: or will it be oliver, the 10-year-old beagle, weighing in at 38 pounds. >> got a little bit of a belly. >> reporter: oh, you have a belly. i might not be boot camp but it is a sort of a paw camp, at the norris animal inn in new jersey. these dogs are put through a

fitness resume like they've never seen. there's the pool. there's group play, which, at first, seems like group sit around like fat lumps. there's even the doggy treld mill. now, this might all look a bit over the top. but the obesity plague for our pelt pelts is way over the top. >> 54% of all dogs andats in america are not classified as overweight or obese. that equals 93 million dogs and cats. >> reporter: big, but maybe getting smaller.ar hits the sta swims a lap and olly and lucky enjoy the treadmill. this is worth noting this is just a day camp, which is a problem, because, at home -- >> give you the face and beg and i felt so sorry for him. i guess i'm killing him with kindness. >> reporter: it's a problem that's all over the country. not your pet's fault if he's fat? >> definitely not. i've net to see a dog that orders an extra shake or fries. >> reporter: camps like this can

cost about $200. and while the activities they do here might look different than what you do at home, vets say an active life and smart diet can achieve the same goals. four weeks into the camp, we have seen it all. doggy massages and stretches. doggy yoga. and bar jumping. but at last, it's time. time for the final weigh-in. first up, it's chase. >> 27 1/2 inches. 84.2. >> reporter: he dropped nearly six pounds. two and a half inches off his waist. his owner? thrilled. >> i saw him in the door over there, i'm like, who is that? >> reporter: sugar and possum? about half a pound and a pound respectively, but both a couple of inches off the waist. now, mom is promising to do her part. >> i've started giving them vegetables. they like string beans. >> reporter: and lucky? he lost close to four pounds. >> he's more active.

he's running instead of just trotting along. >> reporter: and finally, oliver. >> 35.6. >> reporter: almost three pounds gone. 7% of his body weight. and? oliver, you lost three inches on your waist, oliver. you can fit into a whole new pair of pants. since camp ended, most of the docks have maintains most of their weight loss. but lucky is the star of the show. he's lost an additional ten pounds. fit and furry. i'm john berman for "nightline" in morristown, new jersey. >> we checked with the owners tonight. be happy to know that lucky, oliver, the rest, have all kept the weight off. good dogs. and when we come back, dolly parton, on what it's like to hear her song, "i will always love you," become a yueulogy fo witne whitney houston.

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and now, the biggest thing to ever come out of locust ridge, tennessee. dolly parton has written thousands of songs over the years, but the one we've been hearing most has a sad association. tonight, she talks about whitney houston, and the musical power of acrylic fingernails, in this, the "nightline" play list. ♪ and i will always love you ♪ i will always love you >> i wrote the song back in 1972

and it was based on a relationship that i had with porter waggoner. he had the number one syndicated television show in the country, at that time. but whitney is the one that took it worldwide and really made it a household word or song, i should say. kevin costner had loved the song and they were looking for a song to use in "the bodyguard." a month went by, didn't know anything. i was just in the car and then all of a sudden i went into the "i will always love you." ♪ and i >> and i thought i was -- it just everwhee overwhelmed me. i was watching her funeral. i was in tears, as everybody else, just shattered me to hear that song played under those

conditions. when they lifted her coffin up and that song -- i thought my heart was going to stop. it just -- it just pierced me like a knife. ♪ my mother was a great singer. she would sing all the great old songs that i sang so many of them, like -- ♪ pretty fair miss out in the garden ♪ my mother could also play guitar, auto harp, the mountain instruments. but she mostly had her hands full with all the kids, so, she usually just sang. music with 12 kids, poor, country people like so many in the smocky moky mountains. my mother would not allow us to say poor. there are a lot of people worse off than we are. ♪ because you're mine ♪ i walk the line i love "i walk the line." that has been a great one.

i loved everything johnny did. he's a great song writer. he was my first encounter with -- i didn't know until later, exactly what it was, but he was so magnetic and that's when i found out what charisma and magnetism was. he had this way he moved his shoulder and i guess he was on drugs, but he still had it and it was still sexy and still got to me. ♪ "stairway to heaven" is one of my favorites. i love led zeppelin. my husband is a led zeppelin freak. he loved that song. i would hear it all the time, him playing it, all through the years we've been married, for 45 years. and one day i thought, well, i'm going to record that, because that really has a pretty melody. i could kind of gospel it up a little bit. so, i thought i would do it and surprise him with it. so, i did record it. and he didn't particularly care for my version of it. to him, there's only one version

and that's the led zeppelin version and that's how everybody else feels. i can't believe you had the nerve to even do that. ♪ when i do "9 to 5" on my nails. well, that was my poor man's tap writer when i was working on the movie. anyway, i just used this as my little percussion. i played it on the record, too. i said, let me just put it on so i can say, nails, by me. ♪ working 9 to 5 ♪ what a way to make a living ♪ ♪ you can use your mind ♪ and they never give you credit ♪ ♪. >> her new dvd and cd set called "an evening with dolly" is available exclusively at cracker