Then you've got people like Billy Barkhurst or Paul Rugg who are experienced in voice acting, but tried to get into puppetry later on (much like Fran). Or, in Marilyn Sokol's case, she may not have been able to get the hang of the puppetry aspect, but Jim liked her voice enough to keep her on specifically to dub for female characters like Ma Otter, or even singing voices like Betty Lou in "I Want a Monster to Be My Friend." That says something about Jim, who usually required you to be able to do both - voice and performer, not just one or the other.