ASUS Padfone: a video teaser reveals that there will be a third accessory

If we thought that ASUS Padfone meant "only" a smartphone into a tablet, something new could surprise again. ASUS has released a new teaser video, with the sole purpose of increasing attention on the event to be held all'MWC 2012.

The video is short but clear: Matryoshka and slogan "1 +1 +1 = endless possibilities." What will be the third accessory is not even nominated? A physical keyboard Prime Transformer-style to complete the trio? Or some other completely different kind of accessory?