Cook scored a touchdown from 5 yards out, rolling a Texans defender off his back and stiff-arming another on his way into the end zone.
O'Neill looked over his right shoulder and paused, as if to say: "Did he really just do that?"
It's a reaction that's become routine for the third-year offensive lineman when he sees a Cook run on the scoreboard replay.
That's also a common response NFL-wide to the damage Cook has done through the first four weeks of the season. He leads the league in rushing with 424 yards on 75 attempts (fourth most).
What's most impressive is the way he's earned those yards. He leads the NFL with 25 rushing first downs and six rushing TDs. And he has 269 rushing yards after contact, forcing 21 missed tackles on runs, both of which are a league-high, according to Pro Football Focus.
Against the Texans, Cook forced nine missed tackles on runs, the second-most by a running back in a game this season.
"I always wanted to be an all-around running back," Cook said. "I'm not the biggest running back, but I always wanted to carry myself as such, if I was the biggest running back. Breaking tackles is another way to get my team extra downs, to get my team a chance to go score a touchdown. So whatever I've got to do, I'm going to put a lot on the line for this team."
Cook keeps highlights of another all-around back on his iPad for inspiration.
"I've got some Barry Sanders highlights on my iPad, and it's like the old Pitt Draw," Cook said. "Barry just stands there, they hand it to him, and he just shakes the whole team and runs just to go score, and that was pretty much every play he did that. And I watch it -- not because it's Barry Sanders -- I watch it because how he sets his runs up, how he develops things in his mind.
"And I kind of see it from a clear-eye view, and every time I watch his plays, I see something different from him, and how he sees things. I just want to be as explosive as he was. And I know that's not possible, but I'm going to try to match it as best that I can."
Cook's 27 rushing attempts in Week 4 (130 yards and two touchdowns) tied a career high. Cook, who signed a five-year, $63 million extension last month, prioritized gaining muscle throughout the offseason to be able to sustain his production and help with his recovery.
But there's no denying he feels the after effects of that workload 24 hours after a game.
"That's when it hits you, that Monday morning," Cook said. "When you go home Sunday night, adrenaline is still rushing and you're going to lay down and watch some more football. You wake up the next morning and be like, what happened? But you know that's when you get on top of it. You never overreact. You just stick to what got you to that point the week before and just get through it."
Cook battled with injuries in his right leg during his first two seasons and a banged-up shoulder at the end of last year. The Vikings made a conscious effort to spell their running back to keep him fresh. Upon earning 15 hard-fought yards with 11:27 to play in Houston, Cook was shaken up on the play and headed to the sideline. In his place, Minnesota called on second-year back Alexander Mattison to push through on a 4-yard touchdown.
It's a rotation Cook says helps him and his teammates succeed. So far, that's proven to be the case for the fifth-best rushing offense in the NFL.
"We try to spot him throughout the course of the ball game," Vikings coach Mike Zimmer said. "I think Mattison had seven carries last week or something like that. But when it gets to the end of the ball game, we've got to get Dalvin in there. When the game's on the line, we've got to get him in there because he's so [multi]-dimensional. But Alexander's done a great job, too, when he's been in there."