Elise Cavanna

Well, I believe I was wrong. There were two patients in The Dentist. When WC leaves, then returns, he asks the assistance, "Are there any patients?" Assistant replies, "Miss Mason." I had mistakenly presumed the assistant referred to another, unseen patient, but watching it again, I got the joke. WC has completely forgotten that Miss Mason is in the chair.

So, that writhing actress would actually be Elise Cavanna, who was only in three films, all with WC. Still, she was great in this physical comedy, akin to Zazu Pitts.