There was a play in the Niners game where I was watching Irvin, pre-snap, and he looked like he was goofing off, not ready for the snap. I thought, WTF?! Then the play started and I realized Irvin was on Kraepernick spy duty that play. Sure enough, Kraep rolled out, Irvin moved with him, and then made a heat-seeking missile beeline right to Kaep, and made the tackle for a loss, probably recorded as a sack for Irvin. I'm pretty sure Irvin is in Kraepernick's head, that Kraep knows Irvin by name and number and knows he is one of the very, very few D players who can run him down.
A less-noticed part of "The Tip" that sent Seattle to SB48 was Irvin spying on Kaep on that play and basically inducing him to make that throw instead of keep it and run. Having Irvin in there on spy duty was huge.