EDEN PRAIRIE, Minn. —Adam Thielen's study habits aren't at their regular-season level yet.

The Vikings receiver is familiar enough with the players in the Seahawks secondary to know that they should present a challenge and an opportunity. * *

During the regular season, NFL teams use in-depth scouting reports and scout teams to shape practices according to an opponent's tendencies. Players often spend time studying film on the player he is most likely to match up with each week.

That's not so much the case during the early preseason, even though Minnesota did do more card work during Wednesday's practice.

"Yeah, we don't spend a whole lot of time [scouting preseason opponents]," Thielen said. "I think today and tomorrow are days that we kind of focus on that, but it's not like the season where you're going to spend a whole week looking at corners, at defenses and seeing what they're doing.

"We still want to know what they like to do and still want to win," Thielen said. "For us, we're going to treat these next couple of days like a game plan."

Thielen has played the Seahawks in the preseason, regular season and postseason. He did not have a receiving target in December 2015 or the Wild Card game in January 2016, but he did play 20 offensive snaps and 10 special teams snaps a year ago and led Minnesota with four catches for 61 yards.

This time, he'll enter the game having established himself as a starter with 67 catches for 967 yards last season.

Seattle's secondary includes five-time Pro Bowler Earl Thomas at safety and four-timer selections Richard Sherman at cornerback and Kam Chancellor at the other safety spot.

"I think it's huge for me personally," Thielen said. "I think it's a chance to get better, a chance to go against somebody other than your own defense that you see every day and know what they like to do. I think it's going to be an opportunity to get better, and that's all you can ask for."

Expecting the unexpected: Each year, rookies are wowed by "Welcome to the NFL moments" at multiple milestones like first practice and first preseason game.

In addition to catching two passes, including a 2-yard touchdown in his NFL debut last week at Buffalo, fifth-round pick Danny Isidora totaled 11 yards on two punt returns and signaled for a fair catch on another one.

There was a twist, however, when Taiwan Jones hit Adams and was flagged for unnecessary roughness. It turns out that Adams wasn't the most surprised player or spectator.

"I was actually anticipating it because it was happening in other preseason games," Adams said. "I was like, 'I know someone is going to mess up in this game as well,' so when I caught it, I was like, 'OK.' When he hit me, I was like, 'This is what I was waiting for.' "

Adams said he's "come a long way at catching punts" since arriving in Minnesota in May.

"When I first got here, I was terrible," Adams said. "I couldn't track the ball as good, but it just comes with practice. There's really no trick to it, just stay square and track the ball."

The Vikings — and the league — know what Marcus Sherels can do as a punt returner, so they opted to give opportunities last week to Adams and fellow rookie Stacy Coley, who returned one punt eight yards.

Sherels also handled kickoffs earlier in his career, but Adams handled all kickoff return duties last Thursday, returning three for a total of 65 yards.

"I know that we've got Sherels in the hole, but we're trying to look at these young guys. Rodney Adams and Stacy, both," Vikings Head Coach Mike Zimmer said in a session with beat writers. "But honestly, I mean, this team may change. We forget there's going to be cuts and trades and other stuff, too. I mean, we're constantly monitoring that and constantly monitoring other positions."

Zimmer said fielding punts is tough, but experience and gumption help.

"You have to have some courage back there, with guys running at you," Zimmer said. "It's nice to get guys who have done it, at least in college. That's part of this deal in the game, the preseason."

No blanket policy for fourth downs:A situation in Wednesday's practice forced the offense to go for plays on multiple fourth downs. The second-team offense moved the chains against the second-team defense, but a heave into the end zone **was knocked away**.

Zimmer was asked if he plans to be more aggressive on fourth downs when they are optional this season.

"Depends on the situations," Zimmer said. "Really it depends on the team we're playing, the quarterback, the situation of the game, their quarterback. To me, that's always the telltale sign. You know, I'm aggressive by nature, but I couldn't tell you right now if I'm going to go for it on fourth down."