A question about Dog's Ear

Hi all,
I finally started GMing BWG and I already found something I don’t understand (yay me!).

One of my player’s character has the spell Dog’s Ear (he’s a conman with the Gift and wants to be able to overhear useful conversations).

The manual says the spell’s Ob is “Perception” but… whose Perception? Not the PC’s I assume (or the spell would be more difficult as the stat goes up, which doesn’t make much sense to me). How does it work?


The Ob is the Perception of the target of the spell. The idea is that the better your Perception is, the harder it is to enhance.