. tonight on "nightline," dangerous games. from car surfing to drinking hand sandtizer, to st cinnamon challenge and vodka shots in the eyes. why young brains can be souch dangerous places. tonight, risky business. a stunt territory ageing. nic wallenda dares to do what no one ever has, walk across niagara fal falls. we go on the high wire. megastunt and abc news exclusive. and meeting lebron. he's battling for his first nba choim. out of the spot spotlight,

superstar lebron james, how the king of the court is granting one boy's wish. good evening. i'm terry moran. more than 72 hour hs of video are up loaded to youtube every minute. over 3 billion hour hs of video are watched every minute. lot of that seems to be pranks and dangerous stunts performed by teens gleefully avoiding that warning don't try this at home. why do they do all that and why are there so many copy cats. here is abc's john donovan. >> reporter: kids doing stunts has always been with us, but some of it very dangerous stuff indeed. but never has there been so much video of it, showing them actually doing it and making it easier for others to copy it.

>> here we go! >> get ready, curtesy of youtube, mouth full of cinnamon, open wide, here it goes, and here's the brown smoke, cinnamon cloud. this time it was just the other day it was a celebrity that's 15-year-old macy williams, game of thrones, so macy joins a long line of teens and preteens can't resist, the cinnamon challenge, swallow o spoon full in under 60 seconds, nobody can. this kid did, whoever was there egging him on, couldn't believe it. you have another step forward, social media, copy cat videos. stupid stunts, dubious let's call them. quick leap, and stuck with fire. but there's an apparent human attraction. putting our bodies into

dangerous places and then to tape it and up load it. >> some folks feel like celebrity in your own neighborhood or backyard. >> youtube is responsive to the perception, daredevils favorite posting place, it's where kids will get the ideas to try some of this stuff themselves. in a statement youtube told us, youtube's community guidelines prohibit videos intended to encourage dangerous activities that risk serious physical harm. we review video flagged by our users around the clock and routinely remove or age restrict material according to these guidelines. with the community of users up loading 72 hours of video every minute, seems impossible task. like this one, called car surfing, it's nearly half a million hits alone. it's become a bit of a crave these days, yet 16-year-old from florida did not learn about car surfing from youtube. in april, a friend encouraged

her to do it, she nearly died. >> the girl driving flu past the stop sign on to a turn on my road and i was off the back of the car. >> she wears a helmet pieces of her skull were surgically removed. it's the end result of three weeks induced comma following an accident she remembers nothing about. >> i'm disappointed for myself for the choice i made. i'm normally not like that. it was just -- it was stupid decision that we made too fast. >> hannah also wants to persuade young people from making the same mistake she did. she's become an advocate for car and road safety. >> another trend, look at these recent productions. kids ingesting hand sanitizer. it's not nasty tasting too much can actually be toxic. especially now when there's some older kids are doing, mixed with salt for a chemical reaction that produced high-proof alcohol. >> we have patients coming into

the emergency department with these kinds of symptoms, slurred speech, lack of balance, changes in their mental state. >> one video result in thousands of immate tors. it's what we mean by copy cat. >> you feel more special if you think other people are seeing it. some people feel that way. i think it's a very natural human drive for recognition. >> so what? the so what is the kids, particularly in that early adolescent age brain, human brain judgment has a long way to go before it's consistently making the right call, such as don't do something like this at home. this year rgs in facts the cinnamon challenge became so popular, that schools were sending home notes alert parents to the danger. what's interesting this is not just about the teenage craze. judging by the number of

nonsteens pouring shots of vodka into their eyeballs. then it's perhaps another side of brain science that comes into play. >> there's some theories, studies suggest you have to sort of keep tightening the level of risk in order to feel that buzz, kind of like drug addiction. start off with something mundane, and then you may be more and more prone to up the anti-to feel that high or that specialness. >> specialness, perhaps, but when there are so many people doing cinnamon, literally thousands on youtube by now, when does this become the opposite of special? i'm john donovan for "nightline" in washington. really don't try that at home. thanks to john donovan for that. coming up, count down to an incredible high wire act. nic wall len da, practices tonight walk across niagara falls tomorrow.

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in just a few hours, high-wire artist, nik wallenda, will attempt to do what no one has ever accomplished, cross niagara falls on a high wire. >> wall len da, family, is wired for risk, you might say. bill weir is on the u.s. side of the falls where the historic quest will begin. >> reporter: greets from one of american's great natural wonders. that is niagara's horseshoe falls and this is the wire. two inches in diameter, a third of a mile long, and this is the rout nic wallenda hopes to take into history a few hours from

now. facing a few family ghosts along the way. >> reporter: this is the view from the wire. a perch where the average person's throat tightens, pulse quickens, and visionary rows. but not this person. in fact, this is where nic wallenda comes to relax. >> you know, i'm gotten on a wire before when i've had troubles, problems going on whatever, i get on that wire and it's gone. all the troubles of the world are gone. >> but before he can enter that zen state tomorrow night, nic is swinging from intense last-minute focus, to self pinching euphoria. >> i feel like a little kid. >> this wire this and this spot caused him years of planning, personal fortune. he had to convince the u.s. and canada to change 100-year old laws against this kind of stunt

and hire an army of engineers to string the cables. all to try an idea that popped into his 6-year-old brain over tu can falls. >> you folks were performing nearby. >> we were performing in buffalo new york and we came to see the falls. me and my sister looked across and my thought was, awe awesome walk a cable across niagara falls. ie chronic, it's in my blood. >> he is the seventh generation of a fundamentally that's been tempting death to thrill crowds for over two centuries. it all began with nic's great grandfather, carl, architect of the seven-person chair peer immediate performance. 35 feet up, no net. 1962, after one misstep, the pyramid collapsed, two family members died and one was paralyzed. but the next day, with broken

bones and a broken heart, carl snuck out of the hospital so he could make that night's performance. >> wait until you nail they down. >> the wallenda patriarch stayed on the wire until he was 73, until this fateful moment, he tried to cross between two hotels in puerto rico where he lost his balance and then his life. >> i still remember my dad's living room, the couch i was sitting on at age 11 when i saw your great grandfather fall in puerto rico. it sered into my young brain. wow! then to understand that your family kept going regardless of how many wallenda's have tied. explan that to me. >> through triumph and tragedy, one name will always continue, wallenda. >> this is not like a family member dieing in a car accident

and you keep dying. this is a choice. >> what people don't realize, this is a calculated risk. i've trained through winds 55 miles an hour. there's not winds over the falls. the entire process from the get goe was overcoming challenges. my great father taught us to never give up. this is the purest form. >> he carries a supreme confidence, walking the wire since he was actually walk. he was performing professionally around the world at 13, proposed to his wife and eight generation acrobat in the middle of a high wire stroll. >> doing good. look straight ahead. >> now they are teaching their kids the family business with the encouragement of grandma jenny. >> take a bow. that's what we always had to do. >> she lost her husband in that detroit fall in '62 and later riding atop of this pyramid,

tasted the pain that comes with one misstep. >> at age 84, she'll still go for the family occasional stroll, wallenda style, the backyard is one thing, opening old emotional wounds is another. >> you feel all right? >> i'm good. >> last year for danger by design on the science channel, nic and his mother went back to puerto rico, back to the place where carl fell to his death, and he completed the journey, his great grandpa never did. but his proud as he is of his name, nic tells me tomorrow night deliberate attempt to break free of the legacy of wallenda tragedy, go big, get famous, and stay perfect. >> never fallen. >> never fallen. >> broken two bones in my entire life and that was playing football and tennis. so i don't foresee myself flipping or falling. that's where the training comes. accidents are called accidents for a reason.

i trained for that. i trained since a little boy to grab the wire no matter. >> safety harness. he reluctantly agreed. there's no felling how it will affect his performance. there's the wind, the mist, even nesting falcons in the area, known to swoop and attack. you can see the entire knuckle whitening spectacular, starting at 8:00 tomorrow night right here on abc. join us if you can. >> that looks intense. looking forward to the big show tomorrow. coming up, as he tries to win his first nba ring, why lebron james's best moves may be off the court. who built it. this taurus is pretty serious. i can't believe they're actually going to let me drive it. all right, it's got what? 360 horsepower. 365 horsepower. let's see what that feels like. so this is 365 horsepower.

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day two of the nba finals between the miami heat and oklahoma thunder miami heat winning. lebron james trying to win his first nba game. for one young man, lebron james is already a champion. this special relationship, part of the week-long series, my wish, which begins july 15 mt. >> reporter: when he's not shooting hoops, 17-year-old from

peach tree, georgia, likes to check out his bedroom wall, dedicated to lebron james. >> right here, this is my basketball poster. we had a project for art class, and we had to do our favorite athlete or favorite person, i did of course lebron james. you guessed it. >> reporter: once a malnourished infant, in rio, he was adopted by an american family work at his game. but at age 15, diskofrt after practice raised concern. tests revealed the worst. >> he said do i have cancer? and we had to tell him, yes, you do. he asked. am i going to die from this? it was absolutely not. absolutely not. you just kind of watched him deteriorating in front of you. and you just think that you would trade places with him at any point if you could.

now cancer free, he has always dreamed of meeting lebron james. his wish begins to come true in early april, at the american airlines arena in miami, where right next to lebron's locker is his own personalized uniform. tee yag goe is checking out practice when coach erik spoelstra calls him over. i'm thiago. >> with lebron, thiago is part of the heat half-court shooting contest. they move to the three-point line as thiago challenges

lebron. then it's time for these two knew teammates to have a little fun. finally, le brons has an armful of goodiesics like a game-worn jersey for thiago to keep. to remember forever, his special wish. thanks to chris conley for that. lebron james and the heat will be in miami for game 3 of the nba finals sunday night on abc. finally tonight, we've launched or brand new ipad app, abc news. three editions, morning, midday, and prime time, changes as the day progresses from fast headlines in the morning to grips videos at night. our own bill weir took the app for a spin. thanks for watching abc news. we hope you check with good morning america.