What I find weird is that he's still able to sing without all the stuttering, maybe he should sing while speaking so he can make more sense?
Ozzy sings without the stuttering. From the Mayo Clinic Website:
"Stuttering often gets worse when you're excited, tired or under stress, or when you feel self-conscious, hurried or pressured. Speaking in front of a group or talking on the telephone can be particularly difficult.
Although it's not clear why, most people who stutter can speak without stuttering when they talk to themselves and when they sing or speak in unison with someone else."