Nothing wrong with the spell, just the animation.
When you cast it and it's a success it will show the little animation over their head, then the animation goes away and you can't tell if they're still feebleminded or not unless you examine them to see it or you see that they saved.
Curse, Fear, Dance, Hypnotism, ect.. they all get a permanent animation above their heads. Can we change Feeblemind to work this way too please? I'm sure it wouldn't be too hard to alter. Thank you.