Intense enough to turn Catholics into sinners.
Just ask Michigan senior defensive end Frank Clark, who received a warm welcome with his teammates the first time he traveled to South Bend in 2012.
"We pulled up and I've never seen so many middle fingers in my life," Clark said. "I thought I would have seen more at Michigan State. ...I thought it was like a Christian school and I see this big thing of Mary in the middle of the campus.
"I didn't know there were so many people who would flick me off in front of Mary."
And it's intense enough for fans on both sides to wag their metaphorical fingers (though maybe not their middle ones) at Notre Dame coach Brian Kelly, who last season suggested that the rivalry wasn't as "historic" to Notre Dame as some others and was more of a regional rivalry than a national one.
Saturday will be the last time — for at least a few years — normally polite Notre Dame fans will get to show their appreciation for the Wolverines. In 2012, Notre Dame informed Michigan it would opt out of the series, citing its five-game agreement with the ACC as the impetus for dropping one of the most entertaining and fervent rivalries in college sports. Since then, Notre Dame has tried to downplay the significance of the game — but to little success.
Kelly on Tuesday was careful to dance around those comments from last year.
"I'm not going to go so far as to categorize not playing anymore is a good idea, because that's going to come back to me. So I'm going to stay away from that," Kelly said. "I will say this: Given the complexities of our schedule, in not being able to play Michigan, it opens up so many more exciting opportunities for us."
Kelly then concluded his remarks by asking reporters: "How'd I do with that? Pretty good?"
But Notre Dame might not get more "exciting" opportunities than playing Michigan, especially given the topsy-turvy nature the games have adorned in the last five years.
It might not be the most historic rivalry for both teams — they have played every year, save for a few breaks, only since 1978. But especially for younger generations of fans and players on both sides, the rivalry feels as natural and emotional as any.
It's an occasion that always has served as the first true measuring stick for how good each team is and the first time fans are exposed to the pure agony and ecstasy of the college football season.
"That game, playing against Notre Dame is like a feeling in itself," Clark said. "If you never played in that game you don't really know the feeling. You can watch it on TV. You can be there but if you never played in that game, it's the weirdest feeling.
"It's one of those rivalries that's a national rivalry."
Certain rivalries Notre Dame never will give up, those with strong historical ties such as USC and Navy. But the Irish chose to keep alive their series with Stanford — one that doesn't extend back as far as Michigan — to maintain an annual presence in California each year. That meant saying goodbye to Michigan.
Both schools have said they are unsure when the rivalry might resume, and fans have had two years to get used to the impending loss.
Now it's here. It will get a proper send-off: a prime-time kickoff at Notre Dame Stadium in what is likely to be one of the most electric and piercing atmospheres in South Bend since undefeated USC came to town in 2005.
"Its going to be loud. It's going to be real hype," running back Tarean Folston said. "Student section, I know, is going to be crazy. Night game. Under the lights again."
But then the lights will go out without a return date for the first time since 1943, after which the series didn't resume until 1978.
So many memories left behind, and so much more animosity left to share.
Twitter @ChristopherHineCopyright © 2015, The Baltimore Sun