In a split second, the pre-snap read displays myriad tells. Positions of safeties, linebackers, the foot placement of linemen, the show of cover three, cover two, man free or cover zero are all captured by the optic nerve and transmitted to the brain. But how is it processed? How quick can a quarterback adjust if things are switched after a play begins?

The good ones master the synapses and react lightning quick.

Tanner Mangum has the arm. But does he have the mindset to play the chess game thrown at him by Ty Detmer and the pro-style offense BYU deployed the past year?

Head coach Kalani Sitake believes having Mangum, a 13-game starter, back is a very big deal. Detmer, who has loaded Mangum up and plugged him in, says his offense is behind Mangum all the way until the clock says zero.

Games of the mind, programming his head and processing it all with a competitive fire are features Michael and Karen Mangum have seen in their son over the years. If it’s a think deal, he’s all in.

“Tanner is the trivia king of the family,” said Michael. “He watches 'Jeopardy' religiously, he is the Scrabble game champion and master of movie quotes. He can go to a movie once and be quoting lines from it for the next 10 years.”

Karen recently attended a church meeting in which her son gave a talk. “He quoted a quote I sent him years ago on his mission right off the top of his head. I asked him how he remembered it and he said, “I don’t know, I just did.”

After last year's BYU game in Boise, Tanner stayed with his family the rest of the weekend in nearby Eagle, and the family took a bike ride through an upscale neighborhood along the Boise River, where Tanner and his brother Madison had paper routes some seven years ago to earn money for LDS missions.

“We were riding by and Tanner remembered every one of those houses, who lived in them, what their house number was. He was saying, ‘That’s such-and-such lane where the Nelsons live.’ He has an amazing memory,” said Karen, a dietician and nutritionist at a local hospital.

In the Mangum household, Tanner was always challenged by his older siblings, daring him to do things they could do, from executing a jump off a ski run to just about anything two big brother could cook up. Even if nervous or afraid, Tanner learned to take the bait and push himself, if not to please them, to prove himself. It was an incubator of test and perform.

One cold winter day, older brothers Parker and Madison bet Tanner he wouldn’t run down the street in his underwear. Without blinking an eye, he took off, returning to their laughter. And payment.

This might be one of the reasons Tanner picked up the burden of replacing the injured Taysom Hill so quickly in 2015 in the opener at Nebraska just months off an LDS mission to Chile. It was a challenge. It led to a dramatic last-second touchdown pass to Mitch Mathews in Lincoln. It was a season he was not supposed to play, but ended up throwing for 3,377 yards and 23 touchdowns with 60 percent completions.

This past week, Tanner joined his family on a whitewater river trip down the middle fork of the Salmon River through some of the deepest canyons in the continent. It’s a trip the family has taken off and on for the past 20 years.

Years ago, all his siblings were in the same raft with older brother Parker the oarsman and captain, the rest were crew. In a show of how Tanner’s concentration rises to the occasion, on this trip all decided to take part in reading a newly released Harry Potter book out loud, taking turns during the 100-mile, five-day trip.

“Tanner has the best English accent of anyone in the family and read his parts from his iPod with a British accent. One day his sister Meredith fell out of the raft on a rapid and Tanner grabbed her with one hand as he held his iPod in the other, refusing to put it down. Finally, Meredith started yelling at him, ‘Tanner, pull me in, a rapid is coming, put that iPod down.’ We still laugh about that,” said Michael.

A year ago this time, a new coaching staff at BYU, a new offensive coordinator and a new system gave Hill the call to start at QB. Mangum became the supportive backup. It took humility and a vision of that role, a lesson Tanner learned early in his life. Three of his siblings have had six ACL knee surgeries, his younger sister Abby, who will play basketball at BYU this fall, has had two.

In Tanner’s junior year, he moved to Eagle from another part of Boise and became part of a great football squad. After an opening win, that team faced its big rival Rocky Mountain and in the first quarter, Tanner broke his collarbone and was taken to the hospital. He returned to the field an hour after his team had lost, went up to his coach Paul Peterson and said he was sorry.

Peterson, displaying great wisdom, told Mangum now was not the time to be sorry or feel sorry for himself. “Now is the time for you to step up and be a leader, not on the field but off. We need you to go out and lift up the other players, be a team captain.” Peterson challenged Mangum and taught him a great lesson. The next day, Mangum talked to his teammates, mimicking what his coach had said, that things happen for a reason. “He completely flipped it around,” said Karen, “He became the biggest cheerleader on the sidelines the rest of the year.”

Tanner made it back on the field for the state playoffs, playing with pins in his collarbone as the season ended in a barn-burner loss to Rocky Mountain. He was there for his friends at the end. This is what Mangum did in 2016 behind Hill, and ended up finishing the season as a bowl game winner over Wyoming in San Diego. It is a character thing, a brain over emotion thing.

A gunslinger, Mangum’s record at BYU shows he’s at his best when he improvises. This was on display in Hail Mary TD pass wins at Nebraska and against Boise State. His career so far has been highlighted by last-second calls to perform.

This was the case the year before he was named co-MVP of the Elite 11 quarterback camp when a late dropout of Nike’s “The Opening” in Oregon led to a sudden and last-second invite. Upon arriving and being put with a team for the 7-on-7 competition, it was evident those athletes from big cities with Division I offers, a collection of stars from inner-city programs, were deflated. “We got stuck with a big slow white guy from Idaho,” was the refrain.

According to his parents, Tanner felt the pressure, he had something to prove and he felt the weight of it on his shoulders. In time, Mangum’s team found itself in the championship finals, which it lost. Afterwards, his receivers approached him and praised his performance. “We had our doubts but your proved us wrong. You belong,” they told him.

“That gave Tanner some validation and it lifted him up,” said Karen. “It was another thing he learned. It is in those settings that he really thrives.”

After tons of work at different summer camps for exposure, Tanner had a hard time receiving an invitation to the Elite 11. He had one final opportunity to earn the call at a late Nike camp at Stanford. Michael and Tanner drove to Palto Alto and stayed in a cheap Motel 6 room the day before the camp. At 2 a.m., Tanner woke up sick with the flu, vomiting. His father gave him a blessing and he fell back to sleep. He woke up four hours later and it was as if nothing was wrong. He went out and performed and got the invite he sought.

“I think that was a touchstone moment for Tanner that has elevated his belief, his faith and has carried him through on his mission to Chile and now as a young man. He is grateful and thankful for blessings in life, for the power of prayer,” said Michael.

On his two-year mission to Antofagasta, Chile, Tanner found himself in the driest place on the planet, the high Atacama desert where there are no trees, no grass and almost nothing grows near the site of the country’s copper mines. He learned to love the company of fellow missionaries and love the people of Chile, but it was tough. When he got home, the minute he got out of the car he was rolling around on the grass for the first time in two years.

Two months later, he found himself in Lincoln, trying to beat the Huskers.

If brain power is finding a way to assimilate and adjust to challenges on the fly, Tanner Mangum has this kind of experience behind him heading into his junior year for the Cougars.

Much has been written and broadcast lately about Tanner coming out about his challenges with anxiety and depression. He has chosen to use his moment in the limelight to educate people about the issue.

Tanner’s anxiety is similar to that of NFL Hall of Famer Steve Young — it isn’t an issue on the field, but comes when the lights are off, the arena is far away and the electric jolt of adrenalin wears off and he is alone. His mind begins spinning, he worries, he sometimes gets depressed and anxious.

“Tanner is a social person. He thrives on being around people. When he wakes up, he looks to be around others,” said his father. “He chomps at the bit to be social and surround himself with others, to be involved, to perform. He is a good social guy and not a good solo guy. He wants to find someone to be with.”

On the field, none of this anxiety is exhibited. His brother Madison, a receiver, says in the huddle in high school, Tanner was always the guy with the lit fuse, eager to get going, inspiring others to get it done, to have fun.

Tanner’s Kryptonite is snakes. When 10, his brother Madison found a garden snake and Michael schemed with Madison to put it on Tanner’s shoulder. Tanner hates snakes. “When he turned and saw it, the look of terror in his face, I’ll never forget. It was the low point in my role as a father,” said Michael. “If anything, it made him hate snakes even more.”

In just over three weeks, the Cougars report to camp, the drag of two-a-days will be on the front burner and demands on the time of QB Mangum will return, a chore he’ll meet with his wide, thousand-watt smile that betrays the Mangum who sometimes struggles when it’s just him and his shadow.

This is an interesting time for Mangum, who, for the first time in a very long time will head into the season as the main man, the guy, the quarterback who is getting all the attention heading into a college season.

Is he up to it?

History says, yes; this situation is right in his wheelhouse. There are no snakes in football.