Bug regarding Deafen

I don't seem to learn deafen for some reason. A spotted snow leopard bites an elite storm giant soldier. A spotted snow leopard's bite maims an elite storm giant soldier! An elite storm giant soldier has a few scratches. c 'deafen' storm You have deafened an elite storm giant soldier! You can't learn the nuances of deafen since an elite storm giant soldier is immune to your attack! An elite storm giant soldier has a few scratches.