Does My Reflection Always Do What I Do? Where Do Shadows Go When the Light Is Off?

S2 E4: Jessy wonders if her reflection always does everything she does. Playing in the Fun House's Hall of Mirrors, they discover nope, reflections don't always do everything you do! Jessy, Nessy and pals are trying to throw a surprise Birthday party for Huge Ian. But when they are practising their SURPRISE part, they notice their shadows keep disappearing.