It is probably linked to one of the npc granting parts of the tome tactic unlocks, just like the ogre in the camp for 'organ solo' in Barak Varr or the bat wing for the alchemist in Troll Country. I haven't found the npc for the boglar ear yet.
If you activate enough of those, you'll get a tome tactic related to the kind of opponent, like beasts, magical beings, etc.