Well again, really, the sneer wasn't occurring as I was fabricating the mouth, it was happening as I was attaching the plates to the foam.
But you are right, I do usually tend to make the bottom plate slightly smaller than the top, always have, it really makes the puppet's head look better that way... but I think I will try adding an additional half-inch of space next time.
But you are right, I do usually tend to make the bottom plate slightly smaller than the top, always have, it really makes the puppet's head look better that way... but I think I will try adding an additional half-inch of space next time.