It's possible I'm missing something obvious, but I can't seem to "cast" spirit eye; my mana never drops when I click on it, I can't target my characters or anything else for a target. What am I missing?

Thanks

you must "CTRL" click on the portrait of the character that will cast the spell. then bring up the small map and you will see the markings on your map.

It works all right but unfortunately while it shows the location of enemies with red dots, it also shows up every non-hostile bird, roach, fish, butterfly...etc.
Is this really necessary?
I find the main use is for checking the location of switches etc.