The dog's path through the shuddering, quaking library was a winding one. Occasionally he would stop to roll in the bleeding remains of a slaughtered magazine rack or or mark an injured thesaurus as his territory, intent on finding MOTHER but distracted regardless by every exciting new stimulus. In the process, he managed to almost expertly miss every possible encounter with the library's sole remaining nodule of the Old Flesh, the thing you refer to as Isaac.
This was currently fortunate for two reasons. The first of these reasons was that Isaac actually cannot abide dog-creatures, as was passingly established many pages ago - virtually the only character trait Isaac actually iherited directly from the man who once utilized much of his biomass. The other of the two reasons was that Isaac probably didn't need any other distractions right now as he attempted to communicate with Willis. I did say we'd be checking up on these things, didn't I?
There was, fortunately, quite a bit of Willis for Isaac to work with. The Fleshazoid or "Slob" scrambled up the towering mass of veins and arteries to what was more or less analagous to Willis's "head," babbling his curious slob-speech in a desperate hope to snap Willis out of his rampage. As we have also previously established, Willis does not actually understand Isaac as well as either of them believe, but while the situation seemed quite hopeless to the putrid, pinkish eye-creature, there was indeed some small internal aspect of Willis that at least recognized the source of the vocalizations, if not their literal meaning. A frightened and confused little boy, asleep inside a murderous monster, dimly remembering the sound of a dear friend's voice.
Would Isaac successfully break through that haze before Willis and the Professor mindlessly tore each other limb from pseudolimb? In my humble opinion, yes, almost certainly maybe, but enough about all that! Evading one of Willis's roving, blood-hungry sub-tendrils by barely a hair, Nobad had already caught whiff of something new to gnaw apart into gooey spittle-covered chunks, or saturate with his bodily waste, or otherwise defile and ruin as per the natural directives of his kind.
It was a fascinating little piece of something or other. Something that reeked of the fluids and filth of a thousand other dog-things and yet none at all. A facsimile of the scent of dogs. The idea of something dogs have slobbered over and dragged through muck and caked with their dirty little hairs. Yeesh. You life forms really are messed up sometimes. This is all normal stuff to you? Really? You invite these thingies into your homes made of...what now? Giant plant flesh? You build a big box out of the dead parts of other life forms and you just roll around and grow and multiply and excrete in there, huh? Power it with the rotten fossilized fluids of other giant plants? You're probably lucky you and your "Grean Momm" have only been to the Hospital and The Library. I don't think what's left of The Wealds would take all that kindly to you types.
...Where was I? Sorry, there's a lot going on, and I'm still catching up on what I've gotten myself into working with thingies like yourselves. It's a lot. It's really weird. You're really weird. It's almost putting me off how tasty you can be.
But, yeah, the thing. The thing the dog found. It was a stray fragment of something left over from one of your earlier encounters:
The fabric-like severed appendage was still twitching as the concept of life continued to fade. Nobad fully recognized this as the remains of a rapidly less-living thing, causing him to wiggle his anterior knob and pant with obscene amusement at the morbid display, unable to resist giving it a little taste with the wet, squirming muscle that dangled from his feeding orifice. Ugh, you have one of those too, don't you? Revolting, for sure, but with his rudimentary branchination, this act of sensory analysis flooded the thing's brainflesh with a complex mix of memories that were not, by your definitions, necessarily his own...