The revving of the snowmobile engine instantly sent his heart racing.
It was a haunting sound Wade Moore hadn't heard since that night when he hiked down a hill to check on his son, Caleb, who crashed during the Winter X Games competition and had the 450-pound sled roll over the top of him.
On that January evening, Wade held the arm of his son as they walked to the medical tent for treatment, his son telling him how good of a run he had going and how he couldn't wait to take another turn.
Those were some of the last words he heard from Caleb. His son died a week later from internal injuries he suffered in the crash, the first fatality in X Games history.
Three months ago in Texas, there was that unmistakable noise again: The wailing of a snowmobile's engine as his younger son, Colten, practiced flips into a custom-built foam pit outside their home in Krum.
At first, the father's heart skipped. After two jumps, he felt at ease.
He missed this sound. He misses his son.
"Caleb was just a happy-go-lucky kid living his dream and getting to do the thing that he loved to do basically as his job," his father said in a phone interview with The Associated Press. "I always gave him a hard time, saying, `You don't have a job, you are just playing.' He just laughed and said, `We can't help it if our job is playing."
The outpouring of support has astonished the Moore family, with letters and pictures arriving almost every day. Caleb's Facebook page still receives well wishes from fans, with posts such as, "We miss watching ya Man!!" and "Caleb, you are not forgotten. You are my hero."
"I never knew how many people knew about Caleb and had been affected by him," said his mom, Michele, who delivered a stirring eulogy at the funeral.
Since the crash, Wade and Colten have watched the video a few times, hoping to see what went wrong.
They can't detect anything.
Caleb was attempting a backflip in the freestyle event in Aspen, Colo., when the skis on his snowmobile caught the lip of the landing area, sending him flying over the handlebars. The 25-year-old landed face first in the snow with his snowmobile rolling over him.
Caleb stayed down for quite some time before walking off with help from his father and going to a hospital to be treated for a concussion. Caleb developed bleeding around his heart and was flown to a hospital in Grand Junction for surgery. He also had a complication involving his brain and died on Jan. 31.
"There's something to be said about living every day like it might be your last," his father said. "Caleb was able to do what he loved to do every day."
Soon after Caleb's death, ESPN scratched a snowmobile freestyle demonstration in Tignes, France, so organizers could review safety protocols. The network also ended up eliminating another snowmobiling event, best trick, from its schedule.
"He wouldn't want them to stop doing what they were doing just because of that," his dad said. "That's what has kept Colten going. When I asked him, `Do you still want to ride?' He was right quick to say, `Yeah, I want to ride, because Caleb would want me to ride. When I ride, I feel closer to Caleb."
For Michele, watching Colten climb back on a snowmobile has been difficult.
"But this is what Colten really wants," she said. "No matter what has happened, I'm going to support him."
And for Colten, the decision to ride again comes down to this: His big brother wouldn't want him to step away.
"Be mad if I did," said Colten, who wears a necklace with a cross that belonged to his brother.
It wasn't until July that Colten stepped back on a snowmobile. His first attempt that day had his dad anxious.
"I don't know if I was worried -- it was just seeing Colten back on the snowmobile," Wade explained. "But everything went perfect, just like it was supposed to."
These two brothers were extremely close, best of friends as well as riding buddies. They began as all-terrain vehicle racers, before switching over to snowmobiles as teenagers and quickly rising to the top of the sport. Caleb won four Winter X Games medals, including a bronze a few years ago when Colten captured gold. Caleb had some big sponsors, too, such as Rockstar Energy Drink, Fly Racing and Pro Armor.
He also had a garage full of trophies and trinkets, some resting on shelves, others hanging on walls. Just the other day, the family found more plaques inside Caleb's tool box.
"Brings back memories," Wade said.
Caleb constantly challenged Colten to try new tricks on the course built by their dad, complete with artificial turf leading up to the ramp and a foam pit that resembled an expansive above-ground swimming pool.
Caleb was always an inspiration. Still is.
"Riding makes me happy, because that's when I feel closest to him," said Colten, who separated his pelvis in another crash on the same night of his brother's accident. "I feel like he's riding right there with me."
Asked if there was any reluctance to ride again after the accident, Colten quickly responded, "No. None.
"I know he wouldn't want me to stop," Colten said. "My brother taught me everything, from doing backflips as a kid on the trampoline to helping me learn how to ride a bike. He was always there to push me. He would always give me the nudge I needed. I know he's out there, still giving me that little nudge to go for it."