3 1/2" Child's Miniature German Salt Glaze Stein Surprise Inside Souvenir Mug

I always thought this was interesting cause it's the only one I've ever seen.
German Cobalt Blue Salt Glaze Mini Souvenir Stein Tankard Mug
Like a Child's surprise milk cup, this has a little pixie elf gnome inside at the bottom
Written on the side is Zen Andenken / for a souvenir
Stein measures just 3 1/2" tall, no makers mark