They engage each other in bitter verbal back and forth from their respective posts separated by some 800 miles of the Pacific Coast.
They claim each other's waiver leftovers - not always, it seems, for a competitive advantage but rather in acts of gamesmanship.
The men in charge, Pete Carroll and Jim Harbaugh, have been fierce rivals back to their college coaching days in the Pac-10.
Here we go, it's 49ers-Seahawks Part I this week.
And everybody involved knows the NFC West will likely come down to these two nemeses when this season's all said and done, with a pair of dynamic young quarterbacks leading the way.
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