pulling up the curtain

The act of rolling up one's upper lip, as though it were a curtain, to expose the teeth (often in the fashion of imitating a beaver). Pulling the curtain originated in the Appalachians and is frequently utilized in comedic Vine parodies. Pulling up the curtain can be used to express overwhelming joy, frustration, anger, or a natural response to hearing a banjo.

When Seth told Jennifer they were going on a road trip to the Smokey Mountains, she immediately was overwhelmed with joy and was "pulling up the curtain".