I have heard 9 out of 10 Doctors prefer to operate on Liberals. They have two moving parts, the sphincter and the mouth and they are interchangeable.
I do hope we get either a transcript of a clip of her saying this.
The answer is contained within your post: The mouth is, by it's definition, a sphincter.
Which, of course, explains my deep desire to have sphincter to sphincter contact with Barb Boxhead.
I'll let you fill in the blanks concerning the specifics of that desire but it may be inferred from the initials "KMA"