I dunno. If tribbles start popping out of his back, that's going to remind people of the chestbursters from Aliens
. But maybe they instead attach to his spinal cord and supplement his own intelligence by forming their own little collective tribble mind. We don't know how smart tribbles are, individually. Maybe their entire interior is taken up by brain matter (well, however much of it isn't occupied by gonads.) They could be quite intelligent, and having a dozen of them attached to your spine, making you smarter, could result in a vastly superhuman intelligence.
I think we now know what makes Harrison so damn smart.