Shanahan, who is hard to rattle, couldn't help but laugh.
"You got me by surprise there," the coach said. "Who is this guy?"
"What did you do for New Year's?" Griffin asked.
"I tried to put a good game plan together. I wasn't sure how healthy you were, so it was hard without you calling me," answered Shanahan, still chortling away. "You got me good."
Griffin has hardly behaved like a rookie all season, so there's no reason to think it'll start now as he prepares for his NFL playoff debut. He was as loose as anyone Wednesday, whether it was playfully shoving Jarvis Jenkins into the defensive lineman's locker or simply radiating the smile that has rarely been missing during his initial run through the NFL grind.
It was the first practice for Sunday's matchup against the Seattle Seahawks, the Redskins' first home postseason game in 13 years. If the excitement was getting to either half of Washington's rookie backfield - Griffin or running back Alfred Morris - it wasn't showing.
"I've been playing football since I was 5 years old. I just go out there and go have some fun. That's what I do. So I'm not going to think about, 'It's the playoffs,'" said Morris, who added that he doesn't really care for the attention he's getting for a 1,613-yard regular season bettered only by Adrian Peterson.
The performances of Morris and Griffin has cornerback DeAngelo Hall proclaiming: "These aren't ordinary rookies."
"I haven't seen a moment this year where they've been caught up in the moment," defensive tackle Barry Cofield said, "or they've seemed like the moment's been too big for them."
To a man, the Redskins say the entire team shouldn't be caught up in playoff nerves because they've been playing win-or-else games for nearly two months. Every victory in the season-ending seven-game streak was necessary to get to 10-6 and win the NFC East. Notable stat: Washington is 7-0 since Griffin was selected as a team captain.
Also, it helps that the Redskins have a routine week to prepare for the Seahawks. Griffin will take that over the weekslong wait for college bowl games.
"For bowl games, most of the time you're doing way too much thinking," Griffin said. "Trying to devise the perfect play for the perfect defense. And you get in a game and they do something totally different because they're doing the same thing for the past month. So (this is) like a regular-season game, but with a playoff-game atmosphere."
Griffin gave the latest update on the sprained lateral ligament in his right knee, which caused him to miss one game and has limited his explosive running ability in the two games since he returned. He's still sporting a brace, which he adjusted while stretching at the start of practice.
"A lot of people talk about the limp with the brace," Griffin said. "But any time you wear a brace like that, it's to protect you, so it's going to cause a natural limp. You're not going to be able to bend your knee. ... But at the same time you can still generate power."
Griffin said he's "pretty close" to the point where he's being limited by the brace more so than the actual injury, but that the doctors won't let him go without the extra protection.
"So I try to do as much as I can without the brace," he said with a smile. "And then whenever they find out that I don't have it on, I have to throw it on."
The bum knee has prompted Griffin to refine his play without much of a drop-off. He had a 102.4 passer rating in his first game after the injury, and he ran for 63 yards on just six carries in the regular-season finale against the Dallas Cowboys.
"If anything, the injury's shown me a lot, just from a quarterback perspective," Griffin said. "This game's not easy, but it did show me some things that I can do to make the game easier for myself, easier on my body. Ironically I've done a better job of protecting myself since the injury, sliding, getting down, getting all the possible yards I can and getting out of bounds.
"And sometimes things have to happen like that for you to really, really grasp that, and it's shown me a lot. I don't think I've ever rushed for 10 yards a carry in a game, and I did that in this past game, so that was kind of funny."